bug#28385: ert "should" macros to not be globally visible

[Glenn Morris]

Package: emacs
Version: 25.2
Severity: wishlist

emacs -Q -l ert

Now "should", "should-not", and "should-error" are globally defined as
macros (with no "ert-" prefix). They are only useful inside ert-deftests.
Perhaps they should steal a trick from the similar "skip-unless", which
is not globally visible. The global definition is "ert--skip-unless",
and the ert-deftest macro basically makes "skip-unless" an alias for
this inside the body of a test. This seems cleaner.