Symbian/Linux: Enable building with makefile-based system.
- Autodetect SDK by environment variable EPOCROOT and qt directory below. - Environment::appendOrSet/prependOrSet: Avoid duplicate entries - Rename toolchain enumeration value - Adapt S60ToolChainMixin to new GnuPoc setup, provide routines for all required variables. - RVCTToolChain: Make RVCT detection smarter (Check for RVCT<v1><v2>BIN variable). Set all required variables in case of RVCTToolChain/GnuPoc - QtVersionManager: Detect toolchain and Qt version properly, make S60 device run config accept toolchain. - Modify S60DeviceRunControl to execute 'make sis' - Modify S60Devices::detectQt...() to check for Qt installed into SDK first and symlink as fallback.