ignored-*-p: Match against regular expressions

[shackra]

Buffers are created by other packages that appear on projectile's buffer lists, but they always have
some variation that makes impossible including all possible name cases, thus regular expressions
come handy for this sort of cases. This commit allows *-ignored-*-p functions to work with regular
expressions.

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Thanks!

[shackra]

@bbatsov I have done all the fixes as you requested from the pull request #1177 I had to close that one because, boy, I'm really bad at Git.

Tell me what you think and please don't let this one be forgotten too :P