\pgfmatrix: Optimize out \pgf@matrix@column@sep@N.

Simplify code to handle column separation in pgf matrices:
change \pgf@picminx only once per matrix cell for this purpose.

Signed-off-by: Gábor Braun <gabor.braun@uni-duisburg-essen.de>

tex/generic/pgf/modules/pgfmodulematrix.code.tex

@@ -393,12 +393,10 @@
         \advance\pgf@x by -\pgf@xa%
       \fi%
       \advance\pgfmatrixcurrentcolumn by1\relax % only temporary for the following:
-      \expandafter\xdef\csname pgf@matrix@column@sep@\the\pgfmatrixcurrentcolumn\endcsname{\the\pgf@x}%
-      \ifpgf@matrix@fixed%
-        \expandafter\gdef\csname pgf@matrix@column@finish@\the\pgfmatrixcurrentcolumn\endcsname{\global\pgf@picminx=0pt}%
-      \else%
-        \expandafter\global\expandafter\let\csname pgf@matrix@column@finish@\the\pgfmatrixcurrentcolumn\endcsname=\pgfutil@empty%
-      \fi%
+      \expandafter\xdef\csname pgf@matrix@column@finish@%
+        \the\pgfmatrixcurrentcolumn\endcsname%
+        {\global\ifpgf@matrix@fixed\else\advance\fi%
+          \pgf@picminx -\the\pgf@x}%
     }%
     \fi%
     &%
@@ -416,17 +414,13 @@
       \global\pgf@picmaxy=0pt\relax%
       \global\pgf@picminy=0pt\relax%
     \fi%
+  %
+  % Step 5: Row and column separation
+  %
     \csname pgf@matrix@column@finish@\the\pgfmatrixcurrentcolumn\endcsname%
     \pgf@matrix@row@finish%
   \egroup\egroup%
   %
-  % Step 5: Horizontal gap
-  %
-  \ifnum\pgfmatrixcurrentcolumn>1\relax%
-    \pgf@y=\csname pgf@matrix@column@sep@\the\pgfmatrixcurrentcolumn\endcsname\relax%
-    \advance\pgf@picminx by-\pgf@y%
-  \fi%
-  %
   % Step 6: Protocol and adjust height and depth
   %
   % Step 6.1: Protocol...