Switched to using insert_samples to add samples to tiles

Previously, genfft manipulated the tile.double_samples and
tile.string_samples vectors directly.  This hews more closely to other
code that adds data to tiles, and allows the Tile class to keep data
points in the correct order.
Cleaned up building of genfft with FFT_SUPPORT turned off

Removed genfft from the set of programs built by default in the absence
of the FFT_SUPPORT flag, and placed ifdef preprocessor directives around
all code except those few lines of output that are supposed to appear if
genfft is built in the absence of FFT support.
Merge remote-tracking branch 'origin/fourier_precalc' into fourier_precalc