Merge pull request #64 from smithwinston/master

Fix issues #61 (u_boot_eabi_port typo) and #62 (home directory ownership)
Set default values for variables after reading user config.
Escape exclamation point, as per Issue #60
Improve hg rev probe, set SOURCE_VERSION to an error string if rev probe fails
add Xuebing Wang's patches for U-Boot 2014.04
Keep building U-Boot 2013.04 by default until the dust settles on the new version
Use /bin/sh