Extract CXX flags to common.pri file.
Fix gcc 4.6 build.
Fix crash on getting std::string value.
Merge pull request #1 from evgeny-p/precise-build

Merge pull request #1 from evgeny-p/precise-build:
 * Extract CXX flags to common.pri file.
 * Fix gcc 4.6 build.
 * Fix crash on getting std::string value.