Fix configure not working with custom grep

5e199f4 added a check to make sure
configure is properly parsing the Vim version string, but it doesn't
work if user has installed GNU grep instead of the system one. Fix it to
use the more common `[[:digit:]]` (instead of `\d`), and also hardcode
the path for grep.

Fix #1017

Author: ychin

src/auto/configure

@@ -14903,12 +14903,12 @@ $as_echo "using default" >&6; }
 fi
 
 
-    vim_major_version_string=`grep -m 1 'define.*VIM_VERSION_MAJOR' $srcdir/version.h|sed -E -e 's/^.*([0-9]+).*/\1/'`
-  vim_minor_version_string=`grep -m 1 'define.*VIM_VERSION_MINOR' $srcdir/version.h|sed -E -e 's/^.*([0-9]+).*/\1/'`
-  snapshot=`grep -C2 "Add new patch number below this line" $srcdir/version.c|tail -1|sed -E -e 's/^ *([0-9]+),.*/\1/'`
+    vim_major_version_string=`/usr/bin/grep -m 1 'define.*VIM_VERSION_MAJOR' $srcdir/version.h|sed -E -e 's/^.*([0-9]+).*/\1/'`
+  vim_minor_version_string=`/usr/bin/grep -m 1 'define.*VIM_VERSION_MINOR' $srcdir/version.h|sed -E -e 's/^.*([0-9]+).*/\1/'`
+  snapshot=`/usr/bin/grep -C2 "Add new patch number below this line" $srcdir/version.c|tail -1|sed -E -e 's/^ *([0-9]+),.*/\1/'`
   vim_short_version_string="$vim_major_version_string.$vim_minor_version_string.$snapshot"
 
-  if echo "$vim_short_version_string" | grep -q "^\d\+\.\d\+\.\d\+$"; then
+  if echo "$vim_short_version_string" | /usr/bin/grep -q "^[[:digit:]]\+\.[[:digit:]]\+\.[[:digit:]]\+$"; then
     XCODEFLAGS="$XCODEFLAGS VIM_SHORT_VERSION_STRING=$vim_short_version_string"
   else
     as_fn_error $? "could not parse Vim version: $vim_short_version_string" "$LINENO" 5

src/configure.ac

@@ -4543,12 +4543,12 @@ if test "x$MACOS_X" = "xyes"; then
     [ AC_MSG_RESULT(using default) ])
 
   dnl Set CFBundleShortVersionString of Info.plist
-  vim_major_version_string=`grep -m 1 'define.*VIM_VERSION_MAJOR' $srcdir/version.h|sed -E -e 's/^.*([[0-9]]+).*/\1/'`
-  vim_minor_version_string=`grep -m 1 'define.*VIM_VERSION_MINOR' $srcdir/version.h|sed -E -e 's/^.*([[0-9]]+).*/\1/'`
-  snapshot=`grep -C2 "Add new patch number below this line" $srcdir/version.c|tail -1|sed -E -e 's/^ *([[0-9]]+),.*/\1/'`
+  vim_major_version_string=`/usr/bin/grep -m 1 'define.*VIM_VERSION_MAJOR' $srcdir/version.h|sed -E -e 's/^.*([[0-9]]+).*/\1/'`
+  vim_minor_version_string=`/usr/bin/grep -m 1 'define.*VIM_VERSION_MINOR' $srcdir/version.h|sed -E -e 's/^.*([[0-9]]+).*/\1/'`
+  snapshot=`/usr/bin/grep -C2 "Add new patch number below this line" $srcdir/version.c|tail -1|sed -E -e 's/^ *([[0-9]]+),.*/\1/'`
   vim_short_version_string="$vim_major_version_string.$vim_minor_version_string.$snapshot"
 
-  if echo "$vim_short_version_string" | grep -q "^\d\+\.\d\+\.\d\+$"; then
+  if echo "$vim_short_version_string" | /usr/bin/grep -q "^[[[:digit:]]]\+\.[[[:digit:]]]\+\.[[[:digit:]]]\+$"; then
     XCODEFLAGS="$XCODEFLAGS VIM_SHORT_VERSION_STRING=$vim_short_version_string"
   else
     AC_MSG_ERROR(could not parse Vim version: $vim_short_version_string)