check for regex disabled if PCRE found

[John W. Eaton]

On 29-Jan-2009, David Bateman wrote:

| Just to point out that at the moment the changeset
| 
| http://hg.savannah.gnu.org/hgweb/octave/rev/f1534e248260
| 
| is probably not a good idea.. The regex_match class only uses regex and 
| not pcre as it didn't need any of the advanced features of pcre. 
| Therefore the above changeset effective removes the -regexp option from 
| Fclear, Fwho, Fwhos, etc if pcre is found.

OK, I didn't realize that we were using regex if pcre is available.  I
will undo part of it.  But I think this changeset

  http://hg.savannah.gnu.org/hgweb/octave/rev/08331c2fb00f

is what prompted me to make this change because after I applied it and
finally ran autogen and configure again, pcre wasn't being linked
properly.  I will try to fix it.

jwe