Re: WIP: index support for regexp search

The patch yields spectacular speedups with small, simple-enough regexen.  But it does not do a

good enough job when guessing where to use the index and where fall back to Seq Scan.  This can
lead to (also spectacular) slow-downs, compared to Seq Scan.

I guessed that MAX_COLOR_CHARS limits the character class size (to 4, in your patch), is that
true?   I can understand you want that value to be low to limit the above risk, but now it reduces
the usability of the feature a bit: one has to split up larger char-classes into several smaller
ones to make a statement use the index: i.e.:

Btw, it seems impossible to Ctrl-C out of a search once it is submitted; I suppose this is
normally necessary for perfomance reasons, but it would be useful te be able to compile a test
version that allows it.  I don't know how hard that would be.

There is also a minor bug, I think, when running with  'set enable_seqscan=off'  in combination
with a too-large regex: