Removed a redundant step which degraded performance

There was a redundant step in blockmap_mesh, that used getTexture( <string> ) altough it had the ID available. This was the major cause of the abusive use of getTextureID( <string> ).
After profiling, it is clearly seen that the overuse of string parsing (mainly using memcmp) was solved.
![texture_improvement](https://f.cloud.github.com/assets/4559873/658381/d7b6d186-d5dc-11e2-9089-2dcc20ceaa32.png)