Lots more unit tests and code cleanup
Relevant changes from ChangeLog
o job.c: Print -de error information when running multiple jobs
o var.c: only report error for unmatched regex subexpression
when linting (-dL) since we cannot tell when an unmatched
subexpression is an expected result.
reduce memory allocations in the modifiers ':D' and ':U'
reduce memory allocation and strlen calls in modifier ':from=to'
in the ':Q' modifier, only allocate memory if necessary
improve performance for LazyBuf
reduce debug logging and memory allocation for ${:U...}
reduce verbosity of the -dv debug logging for standard cases
fix double varname expansion in the variable modifier '::='
o var.c: avoid evaluating many modifiers in parse only mode
in strict mode (-dL) many variable references are parsed twice,
the first time just to report parse errors early, so we want to
avoid side effects and wasted effort to the extent possible.
Lots of new unit-tests increase code coverage.
Lots of refactoring, cleanup and simlpification to reduce
code size.
Fixes for Bug 223564 and 245807
Updates to dirdeps.mk and meta2deps.py
