fixed 2 warnings with -Wsign-compare
Bugfix: free did not work  when using coalescing

 - local variable "threadcount" did shadow a class member
 - better syntax highlighting in my VIM would have made this more
   obvious :(
 - `-Wshadow` would have warned about it :(
Merge pull request #66 from slizzered/bugfix-wrong_availableSlots_on_coalescing

Bugfix: free did not work  when using coalescing
Merge pull request #64 from slizzered/fixed_uint32_warnings

fixed 2 warnings with -Wsign-compare