Ubuntu 18.04 (not 16.04) is minimum supported OS for YottaDB r1.24 on…

… x86_64

Also fix the ydbinstall script so Ubuntu 18.04 is displayed (instead of Ubuntu 18.4
where the leading 0 in the minor version is lost and could be confusing to the user)
in error messages like the following.

YottaDB supported from Ubuntu 18.04. Current system is Ubuntu 16.04. Not installing YottaDB.

sr_unix/ydbinstall.sh

@@ -346,32 +346,32 @@ if [ "N" = "$ydb_force_install" ]; then
 		osid=`grep -w ID $osfile | cut -d= -f2 | cut -d'"' -f2`
 		osver=`grep -w VERSION_ID $osfile | cut -d= -f2 | cut -d'"' -f2`
 		# Set an impossible major/minor version by default in case we do not descend down known platforms in if/else below.
-		osallowmajorver=999
-		osallowminorver=999
+		osallowmajorver="999"
+		osallowminorver="999"
 		if [ "x8664" = "${ydb_flavor}" ] ; then
 			if [ "ubuntu" = "${osid}" ] ; then
-				# Ubuntu 16.04 and onwards is considered supported on 64-bit x86 architecture
-				osallowmajorver=16
-				osallowminorver=4
+				# Ubuntu 18.04 and onwards is considered supported on 64-bit x86 architecture
+				osallowmajorver="18"
+				osallowminorver="04"
 			else
 				if [ "rhel" = "${osid}" ] ; then
 					# RHEL 7.x is considered supported on 64-bit x86 architecture
-					osallowmajorver=7
-					osallowminorver=0
+					osallowmajorver="7"
+					osallowminorver="0"
 				fi
 			fi
 		elif [ "aarch64" = "${ydb_flavor}" ] ; then
 			if [ "ubuntu" = "${osid}" ] ; then
 				# Ubuntu 18.04 and onwards is considered supported on 64-bit ARM architecture
-				osallowmajorver=18
-				osallowminorver=4
+				osallowmajorver="18"
+				osallowminorver="04"
 			fi
 		else
 			if [ "armv6l" = "${ydb_flavor}" -o "armv7l" = "${ydb_flavor}" ] ; then
 				if [ "raspbian" = "${osid}" -o "debian" = ${osid} ] ; then
 					# Raspbian or Debian 9 or 9.x is considered supported on 32-bit ARM architecture
-					osallowmajorver=9
-					osallowminorver=0
+					osallowmajorver="9"
+					osallowminorver="0"
 				fi
 			fi
 		fi
@@ -382,14 +382,14 @@ if [ "N" = "$ydb_force_install" ]; then
 		if [ "" = "$osminorver" ] ; then
 			# Needed by "expr" (since it does not compare "" vs numbers correctly)
 			# in case there is no minor version field (e.g. Raspbian 9).
-			osminorver=0
+			osminorver="0"
 		fi
-		if [ 1 = `expr "$osmajorver" ">" $osallowmajorver` ] ; then
+		if [ 1 = `expr "$osmajorver" ">" "$osallowmajorver"` ] ; then
 			osver_supported=1
-		elif [ 1 = `expr "$osmajorver" "=" $osallowmajorver` -a 1 = `expr "$osminorver" ">=" $osallowminorver` ] ; then
+		elif [ 1 = `expr "$osmajorver" "=" "$osallowmajorver"` -a 1 = `expr "$osminorver" ">=" "$osallowminorver"` ] ; then
 			osver_supported=1
 		else
-			if [ 999 = "$osallowmajorver" ] ; then
+			if [ "999" = "$osallowmajorver" ] ; then
 				# Not a supported OS. Print generic message without OS version #.
 				osname=`grep -w NAME $osfile | cut -d= -f2 | cut -d'"' -f2`
 				echo "YottaDB not supported on $osname for ${ydb_flavor}. Not installing YottaDB."