2811: Add XSLT plugin capabilities to reconfig for FE and Factory

The user can specify the XSLT plugin directory via the
environment variables GWMS_XSLT_PLUGIN_DIR or the command line
option -xslt_plugin_dir (the latter takes precedence).

When executing reconfig_glidein or reconfig_frontend, the plugins are sorted
and applied (using xsltproc) to the XML configuration file, and the
transformed version is used for the actual reconfig.
2811: Fix missing call to xslt_xml routine
2811: Move xslt_xml into lib function, check for xsltproc
2811: Fix bug -- reconfig scripts use filename, not fd
Release notes for Glideinwms v3_2_1
4590: Add sourcing of sysconfig files to initscripts
Merge branch 'v3/2811' into branch_v3_2
Merge remote-tracking branch 'origin/v3/4590' into branch_v3_2
Checksum for v3_2_1_rc1
Fixed cod for GLIDEIN_Use_Glexec
Now default configuration file is set correctly after upgrade. #4844
Document the xslt plugin usage. #2811
Glideinwms v3_2_1_rc2
updated the docs to describe the -xslt_plugin_dir option to reconfig scripts
2811: Revise the XSLT documentation
Merge branch 'v3/2811-doc' into branch_v3_2
Merge branch 'v3/4546' into branch_v3_2
Fixed typo in the docs
Updated docs for v3_2_1
Glideinwms v3_2_1