Make SyntaxCheckers_*_GetLocList() dictionary functions.
Pass a reference to the current checker to syntastic#makeprg#build().
Add an optional 'redirect' argument to CreateAndRegisterChecker().
Change the sh checker to use the new dictionary functions.
Add a new registry method getLocListRaw() (needed for the sh checker).
Scenario:
- a C file is recognized as having filetype cpp
- run :SyntasticInfo
- run :setf c
- run :SyntasticInfo again
The only checker recognized will be oclint. The reason is, oclint is
registered as a c checker when called from cpp initialization, and that
prevents registering other c checkers when calling ':setf c'.
Solution: always initialize all checkers for a filetype.
