* Background

The 'escape' function in mysqltest, introduced in BUG#32246580,
expects a single character for the first argument. It allows
multi-line strings for the second argument.

* Bug symptoms

If the first argument was a newline character, the test would fail on
Windows.

If the second argument was a multi-line string, the test would fail on
windows.

* Analysis

Windows uses multi-line newline characters.  Therefore, when the first
argument is newline, it works on Linux because newline is only one
character, but fails on Windows because newline is two characters.

In the regular expression library, apparently, the '.'  character does
not match \r, and/or there is a difference between Windows and Linux
in whether \n is matched.

* Solution

Escaping newline characters is asking for portability bugs.  Removed
support for escaping newlines.

Use (?:.|[\n\r]) to match any character including newline. (And switch
to the default regular expression flavor, in order to support (?:...)
patterns).

Also made the regular expression a bit stricter, so it disallows
leading and trailing junk, and disallows space around the character.

And added tests for bad syntax.

RB:25678
Reviewed-By:  <deepa.dixit@oracle.com>
Reviewed-By:  <pedro.figueiredo@oracle.com>