fastcgi: Use pthread_key_t for thread local vars.

Signed-off-by: Sonny Karlsson <ksonny@lotrax.org>
Signed-off-by: Eduardo Silva <edsiper@gmail.com>
Utils: improve stacktrace

This patch adds a few useful features to the mk_utils_stacktrace()
function.

  - It adds the function name resolution and binary file associated
  - The stacktrace is print on any compilation mode
  - Function resolution names are only available on --debug mode
  - If Monkey compiles with --debug mode, the compiler parameter
    -fvisibility=hidden is turned off.

Signed-off-by: Eduardo Silva <edsiper@gmail.com>