Revert changes relative to lib/*.[ch] recent renaming

This reverts renaming and usage of lib/*.h header files done
28-12-2012, reverting 2 commits:

  f871de0... build: make use of 76 lib/*.h renamed files
  ffd8e12... build: rename 76 lib/*.h files

This also reverts removal of redundant include guard (redundant thanks
to changes in above commits) done 2-12-2013, reverting 1 commit:

  c087374... curl_setup.h: remove redundant include guard

This also reverts renaming and usage of lib/*.c source files done
3-12-2013, reverting 3 commits:

  13606bb... build: make use of 93 lib/*.c renamed files
  5b6e792... build: rename 93 lib/*.c files
  7d83dff... build: commit 13606bbfde follow-up 1

Start of related discussion thread:

  http://curl.haxx.se/mail/lib-2013-01/0012.html

Asking for confirmation on pushing this revertion commit:

  http://curl.haxx.se/mail/lib-2013-01/0048.html

Confirmation summary:

  http://curl.haxx.se/mail/lib-2013-01/0079.html

NOTICE: The list of 2 files that have been modified by other
intermixed commits, while renamed, and also by at least one
of the 6 commits this one reverts follows below. These 2 files
will exhibit a hole in history unless git's '--follow' option
is used when viewing logs.

  lib/curl_imap.h
  lib/curl_smtp.h

lib/slist.c

@@ -0,0 +1,127 @@
+/***************************************************************************
+ *                                  _   _ ____  _
+ *  Project                     ___| | | |  _ \| |
+ *                             / __| | | | |_) | |
+ *                            | (__| |_| |  _ <| |___
+ *                             \___|\___/|_| \_\_____|
+ *
+ * Copyright (C) 1998 - 2011, Daniel Stenberg, <daniel@haxx.se>, et al.
+ *
+ * This software is licensed as described in the file COPYING, which
+ * you should have received as part of this distribution. The terms
+ * are also available at http://curl.haxx.se/docs/copyright.html.
+ *
+ * You may opt to use, copy, modify, merge, publish, distribute and/or sell
+ * copies of the Software, and permit persons to whom the Software is
+ * furnished to do so, under the terms of the COPYING file.
+ *
+ * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
+ * KIND, either express or implied.
+ *
+ ***************************************************************************/
+
+#include "setup.h"
+
+#include "curl_memory.h"
+#include "slist.h"
+
+/* The last #include file should be: */
+#include "memdebug.h"
+
+/* returns last node in linked list */
+static struct curl_slist *slist_get_last(struct curl_slist *list)
+{
+  struct curl_slist     *item;
+
+  /* if caller passed us a NULL, return now */
+  if(!list)
+    return NULL;
+
+  /* loop through to find the last item */
+  item = list;
+  while(item->next) {
+    item = item->next;
+  }
+  return item;
+}
+
+/*
+ * curl_slist_append() appends a string to the linked list. It always returns
+ * the address of the first record, so that you can use this function as an
+ * initialization function as well as an append function. If you find this
+ * bothersome, then simply create a separate _init function and call it
+ * appropriately from within the program.
+ */
+struct curl_slist *curl_slist_append(struct curl_slist *list,
+                                     const char *data)
+{
+  struct curl_slist     *last;
+  struct curl_slist     *new_item;
+
+  new_item = malloc(sizeof(struct curl_slist));
+  if(new_item) {
+    char *dupdata = strdup(data);
+    if(dupdata) {
+      new_item->next = NULL;
+      new_item->data = dupdata;
+    }
+    else {
+      free(new_item);
+      return NULL;
+    }
+  }
+  else
+    return NULL;
+
+  if(list) {
+    last = slist_get_last(list);
+    last->next = new_item;
+    return list;
+  }
+
+  /* if this is the first item, then new_item *is* the list */
+  return new_item;
+}
+
+/*
+ * Curl_slist_duplicate() duplicates a linked list. It always returns the
+ * address of the first record of the cloned list or NULL in case of an
+ * error (or if the input list was NULL).
+ */
+struct curl_slist *Curl_slist_duplicate(struct curl_slist *inlist)
+{
+  struct curl_slist *outlist = NULL;
+  struct curl_slist *tmp;
+
+  while(inlist) {
+    tmp = curl_slist_append(outlist, inlist->data);
+
+    if(!tmp) {
+      curl_slist_free_all(outlist);
+      return NULL;
+    }
+
+    outlist = tmp;
+    inlist = inlist->next;
+  }
+  return outlist;
+}
+
+/* be nice and clean up resources */
+void curl_slist_free_all(struct curl_slist *list)
+{
+  struct curl_slist     *next;
+  struct curl_slist     *item;
+
+  if(!list)
+    return;
+
+  item = list;
+  do {
+    next = item->next;
+    Curl_safefree(item->data);
+    free(item);
+    item = next;
+  } while(next);
+}
+