settings: Don't allow dots in section/key names anymore

This requires config changes if filelog is used with a path that
contains dots. This path must now be defined in the `path` setting of an
arbitrarily named subsection of `filelog`.  Without that change the
whole strongswan.conf file will fail to load, which some users might
not notice immediately.

conf/strongswan.conf.5.head.in

@@ -40,12 +40,6 @@ Section names and keys may contain any printable character except:
 	. , : { } = " # \\n \\t space
 .EE
 .PP
-In rare circumstances \fB.\fP characters may be used in section names (e.g. for
-log file names in a filelog section), but should generally be avoided.
-To use \fB:\fP characters in section names (e.g. for Windows log file paths)
-they may be written as \fB::\fP, which the parser replaces with a single
-\fB:\fP.
-
 An example file in this format might look like this:
 .PP
 .EX