Correct locked cell detection (no information means locked).
Merge branch 'master' of ssh://github.com/doy/spreadsheet-parsexlsx
Improve locked cell detection for cells with hidden formulas.  Add test for locked cell detection.
Fix bug-15 test: (merged) cell B2 of the Format sheet is locked.
Add support for optional $formatter argument in parse method.
Merge branch 'pull-25'