Detect IPOpt properly

[[Imported from SVN: r5096]]

m4/ipopt.m4

@@ -34,8 +34,8 @@ IPOPT_INCLUDE_PATH="$IPOPTROOT/include"
 LDFLAGS="$LDFLAGS -L$IPOPT_LIB_PATH"
 CPPFLAGS="$CPPFLAGS -I$IPOPT_INCLUDE_PATH"
 
-# Check whether UG is installed at all
-if PKG_CONFIG_PATH=$PKG_CONFIG_PATH $PKG_CONFIG --exists ipopt; then
+# Check whether ipopt is installed at all
+if PKG_CONFIG_PATH=$IPOPT_LIB_PATH/pkgconfig $PKG_CONFIG --exists ipopt; then
     IPOPT_CPPFLAGS="-I$IPOPT_INCLUDE_PATH"
     HAVE_IPOPT="1"
 else