[fix] gracefully handle no "updpkgsums" in packages hooks

[jmelahman]

Without installed:

$ git commit -m 'foo'
[ buildifier-bin ] setting pkgrel to '1'
[ buildifier-bin ] updating package checksums... FAIL
Command 'updpkgsums' not found. Try installing 'pacman-contrib'.

With installed:

$ git commit -m 'foo'
[ buildifier-bin ] setting pkgrel to '1'
[ buildifier-bin ] updating package checksums... OKAY
[ buildifier-bin ] updating .SRCINFO... OKAY
[jamison/buildifier-6 cc2e0eb] foo
 3 files changed, 10 insertions(+), 6 deletions(-)

[jmelahman]

Thanks for this. We should probably do the same with makepkg and git, too.

Do you mind abstracting this out into a loop that checks these three dependencies, prints out an error message for each that is missing, and then exits with 1 (if any were missing)?

Done

[sudoforge]

sorry this never merged; i have moved on from maintaining these packages. i'll merge this in-tree, but will be archiving the repository shortly.