Re-enable compile as C++ option for libraries as part of making exception work in Symbian, and add pjlib-test to default Symbian build

[bennylp]

This ticket enables C++ compilation option for libraries, as described by ticket #886.

Even though this option is set, the exception framework is still not working on Symbian (that will be fixed by ticket #886).

Also add pjlib-test to default Symbian build.

[bennylp]

In r2768:

• added compile as C++ option in the corresponding MMPs
• also added pjlib-test in bld.inf
• added pjlib-test.pkg
• changed hash.c to hash_test.c in pjlib_test

[bennylp]

In r2769:

• added pj_shutdown() in pjlib-test's test.c
• refactor main_symbian.cpp (it's not been used for a while)
• compilation error/warning about initializing pj_str_t struct from non-constant value

[nanang]

In r2772:

• Minor update: added app registration info for Symbian pjlib-test, so there will be shortcut when installed on device.