make masterdir configurable via configure option: --with-masterdir=<directory>
append masterfiles when CFENGINE_TEST_OVERRIDE_WORKDIR environment is set
sys.inputs is configurable via:
 * ./configure --with-inputdir=<directory> (default: sys.workdir/inputs)
Use the new functions
 * GetInputDir() for inputs directory (sys.inputdir)
 * GetMasterDir()  for masterfiles directory (sys.masterdir)
Merge pull request #1260 from basvandervlies/sys_masterfiles_variable

make masterdir and inputdir configurable via configure options