cp: skip all of the spaces after .if's open brace

This should handle:
  .if 1 \{ .X
  .\}
Reported by Carsten Kunze <carsten.kunze@arcor.de>.
eval: even for "&" and ":", only positive numbers are true

Reported by Carsten Kunze <carsten.kunze@arcor.de>.
char: unlike \s20, \s+20 should be parsed as \s+2\&0

Reported by Carsten Kunze <carsten.kunze@arcor.de>.
ren: .br should flush the current partial word

This patch handles:
  abc\c
  .br
  def
Reported by Carsten Kunze <carsten.kunze@arcor.de>.