Merge pull request #140 from wtsi-npg/master

pull release 76.1 from wtsi-npg master back to devel
lims samplesheet driver bug fix - spiked phix tag index should be defined for plexes; method to return the name of the env. var for the cached samplesheet file; misleading xml lims driver POD entry fixed
Merge pull request #141 from mgcam/devel

lims samplesheet driver update
Merge pull request #142 from wtsi-npg/devel

pull request from wtsi devel to master - release 76.2