[augeas-devel] Speed up computation of regexp difference

[lutter at redhat.com]

Computing the difference of two regular expressions, re1 - re2, involves
converting a finite automaton back into a regular expression. With these
patches, we are a little smarter about it, and first convert strings
embedded in the automaton. That cuts down considerably on the amount of
work, and speeds up difference of regular expressions.

For example, running test_grub.aug through augparse took ~ 5s on my machine
before, and now takes only 3s. This change is important since it does not
only affect augparse, but also augtool, though the speedup is less dramatic
there.

David