Let deps see headers, libs in $SAGE_LOCAL

In particular if OpenSSL development headers are not installed
systemwide, users should be able to install the OpenSSL SPKG for Sage,
which puts such headers in $SAGE_LOCAL/include .

spkg-dist

@@ -145,6 +145,10 @@ if [ -z "$SAGE_LOCAL" ]; then
 fi
 
 cd src
+[ -z "$CPATH" ] || CPATH="$CPATH":
+[ -z "$LIBRARY_PATH" ] || LIBRARY_PATH="$LIBRARY_PATH":
+export CPATH="$CPATH""$SAGE_LOCAL"/include
+export LIBRARY_PATH="$LIBRARY_PATH""$SAGE_LOCAL"/lib
 
 %(install_dependencies)s