[Boost-build] Patch rule string.abbreviate

From: Rick Yang (rick68_at_[hidden])
Date: 2008-05-31 19:04:55

Hi all,

In BOOST_BUILD/util/string.jam, The local variable .abbreviated-$(string)
wasn't define in rule abbreviate.
.abbreviated-$(string) is like cache, but unused.

Best regards,
  Rick Yang