RFC109: fix inifinite loop on metadata substitutions (#4877)
avoid numerous error messages for failed runtime substitutions (#4877)

don't print error messages in regex/validation checks, the higher level
callers already print one out. also add back debugging messages in the
debug logs.
update submodule
WFS 2.0: generate correct MetadataURL element, and add optional wfs_metadataurl_about layer metadata item (#4886)
UTFGRID: implement escaping of item and data values
Fixing a large number of programming errors found by static analysis

issues found by the coverity scanner, most are memory leaks on error
conditions.
Merge branch 'branch-6-4' into master-coverity

Conflicts:
	mapagg.cpp
	mapcontext.c
	mapdraw.c
	mapfile.c
	mapgd.c
	mapgml.c
	maplabel.c
	maplegend.c
	mapogcfilter.c
	mapoutput.c
	mappostgis.c
	maprendering.c
	mapwfs.c
	mapwfs11.c
	msautotest
fixups after coverity merge
Require Validation of SLD ExternalGraphic OnlineResource (#4883)

Onlineresource must validate against "sld_external_graphic" entry of
map->web->validation in order to be taken into account.

added thanks to Regione Toscana - SITA
Fix SDE plugin build (#4887)
Merge pull request #4891 from szekerest/sdefix

Fix SDE plugin build (#4887)
Rename predefined field names for cluster and union layers (#4082)
Merge branch 'master' of https://github.com/mapserver/mapserver into issue4082
Merge pull request #4894 from szekerest/issue4082

Issue4082
add RFC103 layer encoding setter/getter to swig (#4758)
99c0e8b is not needed (#4758)
const-correctness

Add "const" to a bunch of pointers that are not written to.
mapxbase: make DBFIsValueNULL() static

It's an internal function.
simplify SfRealloc()

realloc(NULL,size) is equivalent to malloc(size).  No need for this
runtime check.
remove NULL checks before free()

free(NULL) is legal (no-op).