Protect against comma in pgfkeys arguments

[hmenke]

Motivation for this change

Fixes #389

This should guard against most of the accidental injections of commas through forwarded arguments in pgfkeys.

Checklist

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• Code changes are licensed under GPLv2 + LPPLv1.3c
• Documentation changes are licensed under FDLv1.2

[muzimuzhi]

Though I hardly know anything about some of the touched source fils, to my knowledge of pgfkeys, all changes are at least harmless.

I have some more changes in local branch, and will push them soon.

[muzimuzhi]

oops, not signed

[muzimuzhi]

I made another kind of changes in https://github.com/muzimuzhi/pgf/tree/delimited-args, not sure if it suits the current PR.

Basically what it did is protecting passing an arg absorbed as delimited, to act as a delimited arg again.

 \def\tikz@intersect@name@parse{\pgfutil@ifnextchar[\tikz@intersect@name@parse@opt{\tikz@intersect@name@parse@opt[]}}%}
 \def\tikz@intersect@name@parse@opt[#1]#2\pgf@stop{%
-  \coordinate [#1] (#2) at (\tikz@intersect@@name-\tikz@intersection@count);
+  \coordinate [{#1}] (#2) at (\tikz@intersect@@name-\tikz@intersection@count);
 }%