scm: catch all exceptions at adapter shellout() to fork scm command (#8510, #6713, #4725, #5404).
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 2011-07-10
Parent: [r6229]
Child: [r6231]
