Import bmake-20100808:

Import bmake-20100808:

- boot-strap (TOOL_DIFF): set this to ensure tests use the same version
  of diff that configure tested
- in jobs mode, when we discover we cannot make something, call
  PrintOnError before exit.
- formatting fixes for ignored errors
- ensure jobs are cleaned up regardless of where wait() was called.
- os.sh (MACHINE_ARCH): watch out for drivel from uname -p
- call PrintOnError from JobFinish when we detect an error we are not
  ignoring.
- use bmake_signal() which is a wrapper around sigaction() in place of
  signal()
- add .export-env to allow exporting variables to environment without
  tracking (so no re-export when the internal value is changed).
- fix for .info et al being greedy.
- back to using realpath on argv[0] but only if contains '/' and does not
  start with '/'.