Matches what was added to `fsc` in
a6bbfbdb4e9017e99457d95a32f3e87e7f228d56. Since `fsc` simply wraps
`scalac`, they have identical outputs and syntaxes.
This matches behavior with 'fsc' as committed in
c73673e0f33a6b00e927ff65f366ba25735ad70f last year.
Allows knowledgeable users to supply additional or alternative flags to
get diffferent results from the compiler.
(1) Checkers now have an _exec attribute, and an accessor getExec().
(2) CreateAndRegisterChecker() initializes _exec from an optional argument
'exec'. If this argument is missing, 'name' is used instead.
(3) Functions SyntaxCheckers_*_IsAvailable() are now dictionary functions.
(4) Functions SyntaxCheckers_*_IsAvailable() are now optional. When
they are missing, they are assumed to return executable(expand(self.getExec())).
(5) Argument 'exe' of function syntastic#makeprg#build() is now optional.
If this argument is missing, expand(self.getExec()) is used to set checker
executables.
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).
