eliminate some of the -Wcast-qual warnings (debug-ben-strict target)

  (and that malloc can be called with an int argument).
- Use proper prototypes (with argument list) for various function pointers,
  avoid casts  (however there are still many such cases left in these files).
- Avoid collissions in app_info_cmp if sizeof int != sizeof long.
- Use CRYPTO_LOCK_MALLOC in mem_dbg.c.

 - Made CRYPTO_MDEBUG even less used in crypto.h, giving
   MemCheck_start() and MemCheck_stop() only one possible definition.
 - Made the values of the debug function pointers in mem.c dependent
   on the existence of the CRYPTO_MDEBUG macro, and made the rest of
   the code understand the NULL case.

That's it.  With this code, the old behvior of the debug functionality
is restored, but you can still opt to have it on, even when the
library wasn't compiled with a defined CRYPTO_MDEBUG.

With this change, the following is provided and present at all times
(meaning CRYPTO_MDEBUG is no longer required to get this functionality):

  - hooks to provide your own allocation and deallocation routines.
    They have to have the same interface as malloc(), realloc() and
    free().  They are registered by calling CRYPTO_set_mem_functions()
    with the function pointers.

  - hooks to provide your own memory debugging routines.  The have to
    have the same interface as as the CRYPTO_dbg_*() routines.  They
    are registered by calling CRYPTO_set_mem_debug_functions() with
    the function pointers.

I moved everything that was already built into OpenSSL and did memory
debugging to a separate file (mem_dbg.c), to make it clear what is
what.

With this, the relevance of the CRYPTO_MDEBUG has changed.  The only
thing in crypto/crypto.h that it affects is the definition of the
MemCheck_start and MemCheck_stop macros.

The info removal code was overcomplicated, and error-prone (references being wrongly decreased).  Fixed.

  1. Added code to the memory leak detecting code to give the user the
     possibility to add information, thereby forming a traceback.

  2. Make the memory leak detecting code multithread-safe.

The idea is that we're actually dealing with two separate critical
sections, one containing the hash tables with the information, the
other containing the current memory checking mode.  Those should not
be handled with the same lock, especially since their handling overlap.
Hence, the added second lock.

and make it the default for some debugging configurations.

This is much more helpful than the counter when doing tests with the library
interactively.

a pain to read when using 4-space tabs.

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