Merge(backport) r6230 from trunk (#8825).
scm: catch all exceptions at adapter shellout() to fork scm command.
If scm command does not exist, Linux JRuby 1.6.2 (ruby-1.8.7-p330) raises java.io.IOException in production environment.
Authored by: tmaruyama 2011-07-15
Parent: [r6272]
Child: [r6274]
