Global defines are now documented with references the specification when possible. Removes some redundancy.
Merge pull request #21 from lfasnacht/global-h-rewrite

Improved clarity of src/global.h
Implemented transform skipping (for 4x4 blocks)

transform skip vs. normal transform selection criteria might need more work, currently both are calculated for each 4x4 block and SAD+coeff_SSE is compared.
Added 4x4 SATD (Hadamard)

Taken from HM 13.0
Added new commandline parameter --no-transform-skip
Changed final cost (and transform skip) error function from SAD to SSD
Remove unused variables.

- Working towards issue #11.

- Either removed or redefined variables to not cause a warning.
Check for malloc failure.
Remove unreferenced_parameter macro.

- It was a silly hack to selectively silence compiler warnings from VS, but
  there is no point as it causes compiler warnings in GCC.
Add extra parenthesis to suppress compiler warnings.
Use realloc correctly

Quote from MALLOC(3) manpage:

The realloc() function returns a pointer to the newly allocated memory, which is suitably aligned for  any  kind  of
variable and may be different from ptr, or NULL if the request fails.
Merge pull request #22 from lfasnacht/realloc_fix

Use realloc correctly
Fix typo.

- Obvious typo. This g_bitdepth - 8 used to be g_bitincrement. Doesn't affect
  anything yet as we don't actually support bitdepth > 8 yet.
Resolve unsigned/signed mismatch warnings.

- Working towards issue #11.
Remove unreferenced parameters.

- Working towards issue #11.
Resolve warnings about assignments within conditions.

- Working towards issue #11.
Resolve possible uninitialized variable warnings.

- Working towards issue #11.

- Neither variable was actually used as uninitialized.
Resolve constant conditional expression warning.

- Working towards issue #11.

- I felt that the macro was a little bit too clever in hiding the if-else
  statements so I removed that aspect, which also has the minor benefit of not
  requiring the starting if (0) statement.
Disable warnings for extras/getopt.

- This isn't our code so we don't care about these warnings.
Enable -Wall by default.