bugfixes: lots, including several TLS-related bugs

*) Use a separate TLS key for recursive wrapper entry handling
   The __get_tls() function could possibly require the use of zlib
   or dlopen which, in turn, could attempt to call a wrapped libc
   function which would lead to deadlock.

*) The pthread_atexit handler needed to set the recursive wrapping
   TLS key to prevent deadlock on thread exit

*) Functions being "handled" by the wrapper code needed to properly
   clear and set the recursive wrapper TLS key

*) No reason to close and re-open libraries on fork()

*) Increased log buffer size to 64k per thread

*) Handle stdin/stdout/stderr file descriptor types

*) Proper log flushing on receved signal

Signed-off-by: Jeremy C. Andrus <jeremya@cs.columbia.edu>