share/simple_xls.py: remove rogue print statement in XLSWorkSheet.insert_row().
share/simple_xls.py: cast title to string in XLSWorkSheet.__init__().
illumina2cluster/prep_sample_sheet.py: 0.2.1, new options --include-lanes and --truncate-barcodes (plus some refactoring and addition of tests).
share/IlluminaData.py 1.1.4: fix_bases_mask updated to handle situation when a single index sequence is supplied for dual index data.
share/bcf_utils.py 1.4.5: new function 'walk', traverses directory tree (wrapper for os.walk).
share/IlluminaData.py 1.1.5: get_casava_sample_sheet needs to handle leading & trailing spaces in index sequences.
share/test_bcf_utils.py: added unit tests for 'walk' function.
share/illumina_qc.sh 1.1.1: explicitly specify --extract option for FastQC.

Need to specify the --extract option for FastQC 0.11.2 (though fastq -h suggests that
this is the default behaviour but apparently not) in order to work with QC validation
and reporting. Should be backwardsly compatible with 0.10.1.
Updated ChangeLog after merging from 'devel' branch.