StringUtils::Tokenize: clarify, simplify and optimize
1. pos must be string::npos when lastPos=string::npos, so no need to check pos != string::npos in the while condition. A != a || B != b = !(A==a && B==b) = !(B==b) = B != b
2. as pos needn't be in the condition, it mayaswell be in the while loop.
3. rename variables to reflect what they do.
Merge pull request #4982 from Karlson2k/tokenize_fix_01

StringUtils::Tokenize: clarify, simplify and optimize