Attached patch speeds up ansi-color.  It tries to eliminate as many
allocations (cons and list) as possible.

Benchmarks, recorded in emacs -q, are in the second attachments.  With
the patch applied, there is a 26% speedup in elapsed time, mostly
because the garbage collector has to take care of less allocations.

Two less important side notes:

1) This patch additionally makes it very straight forward to add support
   for ANSI color codes 38 and 48 allowing 256-colors and 24bit
   full-color.  I plan to submit such a patch later (for both ansi-color
   and term-mode).

2) Two vector variables, that were recently added by Jim, were merged
   into one.  Adding him as CC.

Best regards.