Fix compiler warnings on CentOS

Tested with a compiler on a CentOS box and got these warnings. Harmless,
but noisy, so let's fix them.

  compiling matcher.c
  matcher.c: In function ‘CommandTMatcher_sorted_matches_for’:
  matcher.c:181: warning: ISO C90 forbids mixed declarations and code
  compiling watchman.c
  watchman.c: In function ‘watchman_load_string’:
  watchman.c:313: warning: ISO C90 forbids mixed declarations and code
  watchman.c:320: warning: ISO C90 forbids mixed declarations and code
  watchman.c: In function ‘watchman_load_double’:
  watchman.c:334: warning: ISO C90 forbids mixed declarations and code
  watchman.c: In function ‘CommandTWatchmanUtils_load’:
  watchman.c:500: warning: ISO C90 forbids mixed declarations and code
  watchman.c:515: warning: ISO C90 forbids mixed declarations and code
  watchman.c:525: warning: ISO C90 forbids mixed declarations and code
  watchman.c: In function ‘CommandTWatchmanUtils_dump’:
  watchman.c:549: warning: ISO C90 forbids mixed declarations and code
  watchman.c:553: warning: ISO C90 forbids mixed declarations and code
  watchman.c: In function ‘CommandTWatchmanUtils_query’:
  watchman.c:594: warning: ISO C90 forbids mixed declarations and code
  watchman.c:605: warning: ISO C90 forbids mixed declarations and code
  watchman.c:614: warning: ISO C90 forbids mixed declarations and code
  watchman.c:624: warning: ISO C90 forbids mixed declarations and code
  watchman.c:632: warning: format ‘%lld’ expects type ‘long long int’, but argument 3 has type ‘int64_t’
  watchman.c:640: warning: pointer of type ‘void *’ used in arithmetic
  watchman.c:640: warning: ISO C90 forbids mixed declarations and code

Signed-off-by: Greg Hurrell <greg@hurrell.net>
Add casts to silence Clang warnings

Alas, I can't repro these warnings, even with CC=clang and explicitly
adding `-Wformat` to the args. Oh well.

Reported here:

  https://github.com/wincent/Command-T/issues/80

Signed-off-by: Greg Hurrell <greg@hurrell.net>