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/getenv.c

@@ -0,0 +1,61 @@
+/***************************************************************************
+ *                                  _   _ ____  _
+ *  Project                     ___| | | |  _ \| |
+ *                             / __| | | | |_) | |
+ *                            | (__| |_| |  _ <| |___
+ *                             \___|\___/|_| \_\_____|
+ *
+ * Copyright (C) 1998 - 2012, 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 __VMS
+#include <unixlib.h>
+#endif
+
+#include <curl/curl.h>
+#include "curl_memory.h"
+
+#include "memdebug.h"
+
+static
+char *GetEnv(const char *variable)
+{
+#ifdef _WIN32_WCE
+  return NULL;
+#else
+#ifdef WIN32
+  char env[MAX_PATH]; /* MAX_PATH is from windef.h */
+  char *temp = getenv(variable);
+  env[0] = '\0';
+  if(temp != NULL)
+    ExpandEnvironmentStringsA(temp, env, sizeof(env));
+  return (env[0] != '\0')?strdup(env):NULL;
+#else
+  char *env = getenv(variable);
+#ifdef __VMS
+  if(env && strcmp("HOME",variable) == 0)
+    env = decc_translate_vms(env);
+#endif
+  return (env && env[0])?strdup(env):NULL;
+#endif
+#endif
+}
+
+char *curl_getenv(const char *v)
+{
+  return GetEnv(v);
+}