back-port Jamfile version fix from RC_2_0

Jamfile

@@ -18,6 +18,8 @@ ECHO "CXXFLAGS =" $(CXXFLAGS) ;
 ECHO "LDFLAGS =" $(LDFLAGS) ;
 ECHO "OS =" [ os.name ] ;
 
+jam-version = [ modules.peek : JAM_VERSION ] ;
+
 if $(BOOST_ROOT)
 {
 	ECHO "building boost from source directory: " $(BOOST_ROOT) ;
@@ -823,8 +825,10 @@ rule install-paths ( properties * )
 	# package.paths was introduced in boost-1.70 (2018.02)
 	# however, boost build's versioning scheme changed in boost-1.71 to version
 	# 4.0
-	local boost-build-version = [ SPLIT_BY_CHARACTERS [ version.boost-build ] : "-" ] ;
-	if [ version.version-less [ SPLIT_BY_CHARACTERS $(boost-build-version[1]) : "." ] : 2018 03 ]
+	# so, if versions are 4.0+ we want to use package.paths, but if it's a year,
+	# say 2018, that means it's old and we use the fallback below. Any version <
+	# 1990 is considered the 4.0 and later numbering scheme.
+	if [ version.version-less 1990 0 : $(jam-version) ]
 	{
 		import option ;
 		import property ;