free: instead of Curl_safefree()

Since we just started make use of free(NULL) in order to simplify code,
this change takes it a step further and:

- converts lots of Curl_safefree() calls to good old free()
- makes Curl_safefree() not check the pointer before free()

The (new) rule of thumb is: if you really want a function call that
frees a pointer and then assigns it to NULL, then use Curl_safefree().
But we will prefer just using free() from now on.

lib/memdebug.h

@@ -8,7 +8,7 @@
  *                            | (__| |_| |  _ <| |___
  *                             \___|\___/|_| \_\_____|
  *
- * Copyright (C) 1998 - 2013, Daniel Stenberg, <daniel@haxx.se>, et al.
+ * Copyright (C) 1998 - 2015, 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
@@ -171,6 +171,6 @@ CURL_EXTERN int curl_fclose(FILE *file, int line, const char *source);
  */
 
 #define Curl_safefree(ptr) \
-  do {if((ptr)) {free((ptr)); (ptr) = NULL;}} WHILE_FALSE
+  do { free((ptr)); (ptr) = NULL;} WHILE_FALSE
 
 #endif /* HEADER_CURL_MEMDEBUG_H */