It allows to define:
watch("foo_bar.rb") without meaning /foo_bar.rb/ (where "foo_bar_rb.rb" would have been matched)
However, during the deprecation phase, strings that look like a regexes (e.g. "^foo_bar.rb", "foo_bar.rb$", "foo_.*bar.rb" or "foo_(bar|baz).rb" are converted automatically to Regexp and a *very annoying* deprecation message is displayed.
