Accept tcl 8.6 in configure's probe for tclsh.

Usually the search would find plain "tclsh" without any trouble,
but some installations might only have the version-numbered flavor
of that program.

No compatibility problems have been reported with 8.6, so we might
as well back-patch this to all active branches.

Christoph Berg

config/tcl.m4

@@ -4,7 +4,7 @@
 
 
 AC_DEFUN([PGAC_PATH_TCLSH],
-[AC_PATH_PROGS(TCLSH, [tclsh tcl tclsh8.5 tclsh85 tclsh8.4 tclsh84 tclsh8.3 tclsh83])
+[AC_PATH_PROGS(TCLSH, [tclsh tcl tclsh8.6 tclsh86 tclsh8.5 tclsh85 tclsh8.4 tclsh84 tclsh8.3 tclsh83])
 if test x"$TCLSH" = x""; then
   AC_MSG_ERROR([Tcl shell not found])
 fi

configure

@@ -13897,7 +13897,7 @@ fi
 
 # Check for Tcl configuration script tclConfig.sh
 if test "$with_tcl" = yes; then
-    for ac_prog in tclsh tcl tclsh8.5 tclsh85 tclsh8.4 tclsh84 tclsh8.3 tclsh83
+    for ac_prog in tclsh tcl tclsh8.6 tclsh86 tclsh8.5 tclsh85 tclsh8.4 tclsh84 tclsh8.3 tclsh83
 do
   # Extract the first word of "$ac_prog", so it can be a program name with args.
 set dummy $ac_prog; ac_word=$2