Code Cleanup

- Cmake was not updating HAVE_ST_BIRTHTIME.
- NIBBLER_FEATURE_DATE was not properly applied everywhere.
- FEATURE_COLOR was not properly set.
- Some source files failed to include cmake.h, and therefore were not properly
- Removed inefficient use of std::string::substr for guaranteed single character
  strings.
- Integrated Directory::cd.
- Integrated File::ctime, ::btime.
- Integrated Path::operator+.
- Integrated Nibbler::getDigit{2,4,6}.
- Integrated HighResTimer.
  enabling/disabling code.
- All Path objects now expanded internally to absolute form.
- Modified unit tests to accomodate absolute paths.
- Merged new nibbler.t.cpp tests.
- Made various methods const.
- Includes removed from some files, added to others.

test/feature.1013.t

@@ -49,9 +49,9 @@ like ($stderr, qr/^The duration '__' was not recognized as valid, with correct u
 
 # Check that headers are sent to standard error
 $stdout = qx{../src/task rc:outerr.rc list 2> /dev/null};
-unlike ($stdout, qr/^Using alternate .taskrc file outerr.rc$/ms, 'Headers are not sent to stdout');
+unlike ($stdout, qr/^Using alternate .taskrc file .+outerr.rc$/ms, 'Headers are not sent to stdout');
 $stderr = qx{../src/task rc:outerr.rc list 2>&1 >/dev/null};
-like ($stderr, qr/^Using alternate .taskrc file outerr.rc$/ms, 'Headers are sent to stderr');
+like ($stderr, qr/^Using alternate .taskrc file .+outerr.rc$/ms, 'Headers are sent to stderr');
 
 # Check that footnotes are sent to standard error
 $stdout = qx{../src/task rc:outerr.rc rc.debug:on list 2> /dev/null};
@@ -61,9 +61,9 @@ like ($stderr, qr/^Configuration override rc.debug:on$/ms, 'Footnotes are sent t
 
 # Check that debugs are sent to standard error
 $stdout = qx{../src/task rc:outerr.rc rc.debug:on list 2> /dev/null};
-unlike ($stdout, qr/^Timer Config::load \(outerr.rc\) /ms, 'Debugs are not sent to stdout');
+unlike ($stdout, qr/^Timer Config::load \(.+outerr.rc\) /ms, 'Debugs are not sent to stdout');
 $stderr = qx{../src/task rc:outerr.rc rc.debug:on list 2>&1 >/dev/null};
-like ($stderr, qr/^Timer Config::load \(outerr.rc\) /ms, 'Debugs are sent to stderr');
+like ($stderr, qr/^Timer Config::load \(.+outerr.rc\) /ms, 'Debugs are sent to stderr');
 
 # Cleanup.
 unlink qw(pending.data completed.data undo.data backlog.data outerr.rc);