Use `grep -R` to follow apt source symlinks.

In newer greps, '-r' only follows commandline arg symlinks.

http://git.savannah.gnu.org/cgit/grep.git/commit/?id=c6e3ea61d9f08aa0128a0eb13d31a2fbad376f99

closes gh-270
Include the ruby patchlevel in the pre-spec version string.
Set git's user.email and user.name on travis, so the specs can make commits.
Write dep logs to tmp_prefix instead of ~/.babushka/logs when running specs.
No need to regex the separator in SourcePool#dep_for; a string search is fine.
Always reject invalid (non-String/Dep) input to SourcePool#dep_for.

Symbols respond to #[] on >= 1.9 but not on 1.8, and so this caused
inconsistent behaviour with Dep(:symbol_name).
Fix 'babushka edit' command, when EDITOR/BABUSHKA_EDITOR/VISUAL environment variable not set

Without this fix:

$ babushka edit npm
/usr/local/babushka/lib/babushka/cmdline.rb:106: undefined method `which' for Babushka::Cmdline:Class (NoMethodError)
	from /usr/local/babushka/lib/babushka/source_pool.rb:68:in `call'
	from /usr/local/babushka/lib/babushka/source_pool.rb:68:in `find_or_suggest'
	from /usr/local/babushka/lib/babushka/cmdline.rb:101
	from /usr/local/babushka/lib/babushka/cmdline/parser.rb:28:in `call'
	from /usr/local/babushka/lib/babushka/cmdline/parser.rb:28:in `run'
	from /usr/local/babushka/lib/babushka/base.rb:60:in `run'
	from /usr/local/bin/babushka:25
Merge pull request #271 from jwark/patch-1

Fix 'babushka edit' command, when no EDITOR/BABUSHKA_EDITOR/VISUAL env set
Use CONST_CASE for constants
Leave deprecated aliases
Spacing around the VERSION constant.
Convert prefix consts to CONST_CASE too, with deprecations.
Convert remaining internal constants to CONST_CASE. These shouldn't need deprecations.
Update the tick/cross const deprecation date.
Add removal date for deprecated constants.
Print deprecation warnings when the old constants are used.
Merge branch 'const_case'
Add GitRepo#resolve_full, to return the complete SHA.
The GitRepo#resolve SHA will always be 7 chars in the spec; the repo is a fixture.
Add a note to GitRepo#resolve about short SHAs changing.