Added a debug switch to elapsed pattern insertion and pattern reduction times. Upgraded eg/assemble to make use of it.
Tweaked the resulting pattern when it uses 'imsx' flags, giving (?i-xsm:(?:^a[bc]|de)) instead of (?-xism:(?i:(?:^a[bc]|de))) .
Changed the "match nothing" pattern to something slightly less unsurprising to those who peek behind the scene. Bug #18266 reported by Philippe Bruhat.