* minibuffer.el (completion-table-with-terminator): Properly implement

* minibuffer.el (completion-table-with-terminator): Properly implement
boundaries, in case `terminator' appears in the suffix.
(completion--embedded-envvar-table): Don't return boundaries if
there's no valid completion.  Simplify.
(completion-file-name-table): New completion table extracted from
completion--file-name-table.
(completion--file-name-table): Use it.
(read-file-name-predicate): Declare obsolete.
(read-file-name): Use the pred arg i.s.o read-file-name-predicate.
* vc-bzr.el (vc-bzr-revision-completion-table): Use the new
completion-file-name-table, and use the `pred' argument.
* files.el (locate-file-completion-table): Use the `pred' arg rather
than read-file-name-predicate.
(abbreviate-file-name): Use \` rather than ^ for BOS.