allow for expressions in symbol rotation and scale
the single, graduated and categorised symbol renderers have been
refactored to avoid use of raw pointers (auto_ptr are used instead, they
are deprecated in c++11 but the change for unique_ptr is an easy one and
they clearly state the design intend: exclusive ownership)

2 general use function to quote and unquote strings for/from xml have
been added to qgis.h
changed std::auto_ptr for QScopedPointer
fixed bug in rotation & removed xml encode/decode
fixed toSld() & replaced "" by QString
Merge pull request #1075 from Oslandia/expressions_in_symbol_rotation_and_scale_for_pr

[FEATURE] allow for expressions in symbol rotation and scale