[PATCH] tsearch parser inefficiency if text includes urls or emails

Hi,

While playing around/evaluating tsearch I notices that to_tsvector is 
obscenely slow for some files. After some profiling I found that this is due 
using a seperate TSParser in p_ishost/p_isURLPath in wparser_def.c.
If a multibyte encoding is in use TParserInit copies the whole remaining input 
and converts it to wchar_t or pg_wchar - for every email or protocol prefixed 
url in the the document. Which obviously is bad.

I solved the issue by having a seperate TParserCopyInit/TParserCopyClose which 
reuses the the already converted strings of the original TParser - only at 
different offsets.

Another approach would be to get rid of the separate parser invocations - 
requiring a bunch of additional states. This seemed more complex to me, so I 
wanted to get some feedback first.

Without patch:
andres=# SELECT to_tsvector('english', document) FROM document WHERE filename = 
'/usr/share/doc/libdrm-nouveau1/changelog';
                                                                                                      
 ─────────────────────────────────────────────────────────────────────────────────────────────────────
...
 (1 row)
 
Time: 5835.676 ms

With patch:
andres=# SELECT to_tsvector('english', document) FROM document WHERE filename = 
'/usr/share/doc/libdrm-nouveau1/changelog';
                                                                                                      
 ─────────────────────────────────────────────────────────────────────────────────────────────────────
...
 (1 row)
 
Time: 395.341 ms

Ill cleanup the patch if it seems like a sensible solution...

Is this backpatch-worthy?

Andres


PS: I let the additional define in for the moment so that its easier to see the 
performance differences.