Apply the same changes that were applied to html/validator in
vim-syntastic/syntastic#2241 to w3/html so that it can be used to
validate SVG and XHTML as well.
Add support for `g:syntastic_{type}_w3_doctype` to control the doctype
POST parameter sent to the validator. This is necessary for SVG without
a DTD (which would otherwise be validated as generic XML) and useful for
all the types to control validation.
Signed-off-by: Kevin Locke <kevin@kevinlocke.name>
(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).
