write CLASS validation to mapfile (#4596)
Fix issues with wms_layer_group printing (#4533)
Merge branch 'branch-6-2'
update autotests for #4533
update autotests for #4533
Updated msautotest
Enable runtime substitutions using `class` level `validation` blocks (#4600)

 As well as now honouring
class level validation blocks a validation hierarchy is implemented
across `web`, `layer` and `class` level validation blocks.  This
hierarchy *only* takes effect when identical validation keys appear in
`web`, `layer` or `class` such that keys in more specialised blocks
override those in more generalised blocks. i.e. `class` overrides
`layer` which overrides `web`.

In conjunction with the above, default class level substitutions are
also enabled and also implement the precedence rules above. i.e. a
default substitution in `class` overrides `layer` which overrides
`web`.

Ensure validation *always* occurs when a substitution is requested
Fixes #4596
Fixes #4600
update submodule version
update submodule
Implement MS RFC 88: Saving MapServer Objects to Strings (#4563)
Updated msautotest
Fix mapfile writer to write SVG symbols (#4607)
Merge branch 'branch-6-2'

Conflicts:
	mapsymbol.c
	msautotest
Merged previous results in order to dissolve some errors during last git rebase.