[mkgmap-dev] Commit r3875: decrease peak memory and improve speed for global index creation

Version mkgmap-r3875 was committed by gerd on Sat, 01 Apr 2017 decrease peak memory and improve speed for global index creation - use memory cache were it helps and free memory for caches after SortKey are calculated - always free memory for mdr19 data - implement (undocumented) --x-mdr7-excl filter for street name index. Not very useful until user knows special names which should not appear in the street search. - Use new DoubleSortKey instead of MultiSortKey in Mdr7. - Don't compare sort keys byte by byte if both are the same, which is quite likely with the caches http://www.mkgmap.org.uk/websvn/revision.php?repname=mkgmap&rev=3875