Merge pull request alecthomas#84 from zfjagann/regexp

Added support for regexp flags

Pull Get out of Value again to avoid breaking external values.

Add .Counter().

Fixes alecthomas#80.

Use gopkg import to avoid duplicate fetch.

Add app.DefaultEnvars(), flag.Envar(n) and flag.NoEnvar().

Fixes alecthomas#78.

Accidentally nuked a title character.

Fix tests.

Don't re-parse when applying "help" command.

Float32 test with epsilon.

Fix bug in EnumVar (fixes alecthomas#59).

Thanks @johnl, for picking this up.