Remove variables that are set but not used

This fixes build warnings with gcc.
pass each frame timestamp to codec
Don't try to use pow(int,int)

When building for android or older MSVC versions, this makes the build
fail, when it is ambiguous which pow() overload to use, when there
is no function matching pow(int, int).
Use the right data type for some local variables

pDecEngine->uiOffset is an uint64_t as well, and *pSliceNum
is uint32_t.

This fixes warnings about comparison between signed and unsigned
in gcc and msvc.
Add casts to avoid warnings about comparison between signed and unsigned

This fixes warnings with gcc and msvc.
Merge pull request #1486 from mstorsjo/fix-pow-params

Don't try to use pow(int,int)
Merge pull request #1488 from mstorsjo/fix-warnings

Fix warnings with gcc and MSVC
Merge pull request #1485 from ruil2/cabac_refine

pass each frame timestamp to codec
Merge remote-tracking branch 'upstream/master' into travis.osx