avoid extra space intruding rail diagrams (amending 4854f7ee0987);

--- a/lib/texinputs/isabelle.sty	Thu Nov 24 15:21:54 2016 +0100
+++ b/lib/texinputs/isabelle.sty	Fri Nov 25 14:10:33 2016 +0100
@@ -73,7 +73,7 @@
 \newcommand{\isadigit}[1]{#1}
 
 \newcommand{\isachardefaults}{%
-\def\isacharbell{\isamath{\bigbox}}  %requires stmaryrd
+\def\isacharbell{\isamath{\bigbox}}%requires stmaryrd
 \chardef\isacharbang=`\!%
 \chardef\isachardoublequote=`\"%
 \chardef\isachardoublequoteopen=`\"%