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/strequal.c

@@ -0,0 +1,124 @@
+/***************************************************************************
+ *                                  _   _ ____  _
+ *  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"
+
+#ifdef HAVE_STRINGS_H
+#include <strings.h>
+#endif
+
+#include "strequal.h"
+
+/*
+ * @unittest: 1301
+ */
+int curl_strequal(const char *first, const char *second)
+{
+#if defined(HAVE_STRCASECMP)
+  return !(strcasecmp)(first, second);
+#elif defined(HAVE_STRCMPI)
+  return !(strcmpi)(first, second);
+#elif defined(HAVE_STRICMP)
+  return !(stricmp)(first, second);
+#else
+  while(*first && *second) {
+    if(toupper(*first) != toupper(*second)) {
+      break;
+    }
+    first++;
+    second++;
+  }
+  return toupper(*first) == toupper(*second);
+#endif
+}
+
+/*
+ * @unittest: 1301
+ */
+int curl_strnequal(const char *first, const char *second, size_t max)
+{
+#if defined(HAVE_STRNCASECMP)
+  return !strncasecmp(first, second, max);
+#elif defined(HAVE_STRNCMPI)
+  return !strncmpi(first, second, max);
+#elif defined(HAVE_STRNICMP)
+  return !strnicmp(first, second, max);
+#else
+  while(*first && *second && max) {
+    if(toupper(*first) != toupper(*second)) {
+      break;
+    }
+    max--;
+    first++;
+    second++;
+  }
+  if(0 == max)
+    return 1; /* they are equal this far */
+
+  return toupper(*first) == toupper(*second);
+#endif
+}
+
+#ifndef HAVE_STRLCAT
+/*
+ * The strlcat() function appends the NUL-terminated string src to the end
+ * of dst. It will append at most size - strlen(dst) - 1 bytes, NUL-termi-
+ * nating the result.
+ *
+ * The strlcpy() and strlcat() functions return the total length of the
+ * string they tried to create.  For strlcpy() that means the length of src.
+ * For strlcat() that means the initial length of dst plus the length of
+ * src. While this may seem somewhat confusing it was done to make trunca-
+ * tion detection simple.
+ *
+ *
+ */
+size_t Curl_strlcat(char *dst, const char *src, size_t siz)
+{
+  char *d = dst;
+  const char *s = src;
+  size_t n = siz;
+  union {
+    ssize_t sig;
+     size_t uns;
+  } dlen;
+
+  /* Find the end of dst and adjust bytes left but don't go past end */
+  while(n-- != 0 && *d != '\0')
+    d++;
+  dlen.sig = d - dst;
+  n = siz - dlen.uns;
+
+  if(n == 0)
+    return(dlen.uns + strlen(s));
+  while(*s != '\0') {
+    if(n != 1) {
+      *d++ = *s;
+      n--;
+    }
+    s++;
+  }
+  *d = '\0';
+
+  return(dlen.uns + (s - src));     /* count does not include NUL */
+}
+#endif