configure.in: Don't use the dc command unless it is required

Some systems don't have the 'dc' command installed, and this causes
configure to print a warning message unnecessarily for a standard
(non-WIP and non-pre) release of e2fsprogs.

It's easy enough to avoid this problem, so let's do it.

Addresses-Sourceforge-Bug: #1893024
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

configure

@@ -1901,12 +1901,12 @@ esac
 
 base_ver=`echo $E2FSPROGS_VERSION | \
 	       sed -e 's/-WIP//' -e 's/pre-//' -e 's/-PLUS//'`
-pre_vers=`echo $base_ver 0.01 - p | dc`
 
 date_spec=${E2FSPROGS_YEAR}.${MONTH_NUM}.${E2FSPROGS_DAY}
 
 case $E2FSPROGS_VERSION in
 *-WIP|pre-*)
+	pre_vers=`echo $base_ver 0.01 - p | dc`
 	E2FSPROGS_PKGVER="$pre_vers+${base_ver}_WIP_$date_spec"
 	;;
 *)

configure.in

@@ -41,12 +41,12 @@ esac
 
 base_ver=`echo $E2FSPROGS_VERSION | \
 	       sed -e 's/-WIP//' -e 's/pre-//' -e 's/-PLUS//'`
-pre_vers=`echo $base_ver 0.01 - p | dc`
 
 date_spec=${E2FSPROGS_YEAR}.${MONTH_NUM}.${E2FSPROGS_DAY}
 
 case $E2FSPROGS_VERSION in
 *-WIP|pre-*)
+	pre_vers=`echo $base_ver 0.01 - p | dc`
 	E2FSPROGS_PKGVER="$pre_vers+${base_ver}_WIP_$date_spec"
 	;;
 *)