tests/test-config-case.t

util: fix crash converting an invalid future date to string

Post-2038 timestamps cannot be handled on 32-bit architectures. Clamp
such dates to the maximum 32-bit timestamp.

  $ echo '[Section]' >> $HGRCPATH
  $ echo 'KeY = Case Sensitive' >> $HGRCPATH
  $ echo 'key = lower case' >> $HGRCPATH

  $ hg showconfig Section
  Section.KeY=Case Sensitive
  Section.key=lower case