This replaces use of the system time command with __DATE__ and __TIME__
I think the following two errors are caused by fedex_plus being rebuilt for each test:
Linking CXX executable ../../bin/fedex_plus
CMakeFiles/fedex_plus.dir/__/express/fedex.c.o: file not recognized: File truncated
and
[ 87%] Running fedex_plus for AP214E3_2010...
/bin/sh: /opt/step/test-scl/build_ctest/bin/fedex_plus: Text file busy
fedex_plus is being rebuilt because the version string changes, since it contains the date and time.
* Print this info from `p21read -v` and in a comment in generated source, not just from `fedex_plus -v`
* Use a function `const char* scl_version()`, instead of using the macro `SCL_COMMIT_ID`
* Fail gracefully if the `.git` directory does not exist (thanks CY!)
* Fixes issue #89
