improve check for stop-after option: don't accept substring of allowed
parms 

The old code did not complain about --stop-after=problem


git-svn-id: http://svn.mkgmap.org.uk/splitter/trunk@410 838fabe5-b1a8-4b81-9896-7a84386980e9
improve and simplify split algo: 
- Reduce number of tests which are likely to fail
- After maximizing the number of nodes in the least
populated part, try to further optimize the 
solution for the other tiles
- fix error (?): search-limit was not reset to the start value
for each rectangular area when --polygon-desc-file is used. 
The effect was that the search took longer than wanted but also 
returned better results.



git-svn-id: http://svn.mkgmap.org.uk/splitter/trunk@411 838fabe5-b1a8-4b81-9896-7a84386980e9