THEORA_DISABLE_FLOAT C preprocessor symbol.

This originally disabled slow floating point code in the library,
but the critical path code has all been removed. It also used
to disable function of th_granule_time() which returns a double,
but it has not done so since prior to the 1.0 release, and there
have been no complaints.

It might be helpful to restore this option if it eliminated    
the th_granule_time() API entry entirely, so that platforms
without native floating point don't have to link to an emulation
library, but in the absence of a request we prefer shorter code.

svn path=/trunk/theora/; revision=17951

This will be the basis of the 1.2.x releases.

svn path=/trunk/theora/; revision=17445