[Fix #546] Don't make options buffer local by default
Make some options local explicitly [#546]

flycheck-(gcc|clang)-language-standard need to be local because a global
standard would conflict with the major mode (e.g. using a C standard in
a C++ buffer).

flycheck-rust-crate-(root|type) need to be local, because there is no
global crate.  Each buffer belongs to a specific crate.
Set the executable buffer-locally
Update the changelog
Merge branch '546-no-implicit-buffer-local'

* 546-no-implicit-buffer-local:
  Update the changelog
  Set the executable buffer-locally
  Make some options local explicitly [#546]
  [Fix #546] Don't make options buffer local by default

Conflicts:
	doc/flycheck.py