Fix typo in `beaglebone_check_uboot`

The `beaglebone_check_uboot` function was incorrectly calling
`u_boot_eabi_port` instead of `uboot_eabi_port`.
Set home directory owner when using User option

The `User` option allows a user to be created in the target image,
however, while the home directory was being created, it was still
owned by root.

Using the `pw usershow` command, the UID/GID can be retrieved and
used in a call to `chown` to set the proper ownership for the
user's home directory.
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
Merge https://github.com/kientzle/crochet-freebsd