CMake Nightly Date Stamp
CTest: Fix ctest_update with 'HEAD' file in source tree

Add the '--' command-line separator to make the HEAD reference
unambiguous.  Extend the CTest.UpdateGIT test to cover this case.
Fix the cmGeneratorExpression::Split when leading chars are present.

In the case of input like

 foo$<1:bar>

the preGenex should be 'foo'. In that case, the search for a ';'
will not find one, and there is no preceding input to process as a
non-genex list.

Previously, the result of 'splitting' such a string would instead
be a vector containing the same string two times.
Merge topic 'ctest_update-Git-HEAD' into next

78b81b7 CTest: Fix ctest_update with 'HEAD' file in source tree
42c56c8 CMake Nightly Date Stamp
Merge topic 'fix-genex-split-duplication' into next

f93a388 Fix the cmGeneratorExpression::Split when leading chars are present.