[PATCH] [Proposal] [Analyzer] Individual options for checkers

[Aleksei Sidorin]

Hello Ted,

This patch (its current version) implements a helper function to retrieve individual options for checkers. Currently the only way to set options for checkers is a registration of a special checker. I tried to implement a more convenient way to do this. For example,
```
checker->setCheckEnabled(Expr::SET_VolatileRead, getBooleanOption("EmitOnVolatileRead", true, checker));
```
instead of registration of a new checker (Malloc and CString checkers have even macros to do this). It is only a small convenience and doesn't break any existing functionality.
This should also work for groups of checkers. For example, `... -analyzer-config unix=some_option` may be specified to set behaviour for all checkers in `unix` group.

http://reviews.llvm.org/D3967