On save file, if the file is in project, open new buffer with bad filepath so the buffer open is empty.
Before change:
```gcc -c -x ada -gnats src/principale.adb
principale.adb:32:26: missing ";"```
quickfix try to open principale.adb but file is in src/ not in current directory.
After change:
```gcc -c -x ada -gnats -gnatef src/principale.adb
src/principale.adb:32:26: missing ";"```
quickfix open file src/principale.adb.
(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).
