volk: cleaned up 32fc_x2_dot_prod_32fc code. Improved results; fixed on OS X.

- Added unaligned versions of kernels.
- Fixed issues with tail handling
- Use _mm_setzero_ps instead of subtracting to zero out values
volk: fixed issue with size_t comparison of std::string function (compare against std::npos, not -1).
Merge branch 'maint'
Revert "GNU Radio EXPAND macros for template files:"

This reverts commit 6fc200fcba65cc4d18d7b10381da72769c0183c4.

The original commit causes excessive rebuild sensitivity by
regenerating many public API header files at cmake time instead
of at build time.