bug#13892: 24.3.50; Provide for customizing default regexp in hi-lock commands

[Jambunathan K <kjambunathan@gmail.com>]

Juri Linkov <juri@jurta.org> writes:

>> +(defvar hi-lock-read-regexp-defaults-function
>> +  'hi-lock-read-regexp-defaults
>> +  "Function that provides default regexp(s) for highlighting commands.
>> +This function should take one argument OP and return one of nil,
>> +a regexp or a list of regexps for use with highlighting command
>> +OP.  OP, a symbol, can be one of `phrase', `line' or `nil'
>> +signifying commands `hi-lock-face-phrase-buffer',
>> +`hi-lock-line-face-buffer' and `hi-lock-face-buffer'
>> +respectively.
>
> Requiring an additional argument `op' means that we wouldn't
> be able to customize `hi-lock-read-regexp-defaults-function'
> to just `find-tag-default' or `find-tag-default-as-regexp'.
> I think there is no need to distinguish between different
> hi-lock commands since one user would very likely prefer
> the one way to get the default for all hi-lock commands,
> so you could call `hi-lock-read-regexp-defaults-function'
> without arguments.

Committed as bzr revision 111971.

I have removed OP, updated the docstring.  I have also introduced
`find-tag-default-as-regexp' in subr.el.