DLL_HEADER for NGx_Mesh Class

git-svn-id: https://netgen-mesher.svn.sourceforge.net/svnroot/netgen-mesher/netgen@662 38e36fca-e102-11dd-b6c5-65a6809f2f0c
DLL_HEADER

git-svn-id: https://netgen-mesher.svn.sourceforge.net/svnroot/netgen-mesher/netgen@663 38e36fca-e102-11dd-b6c5-65a6809f2f0c
bug fix for memory cleanup for curved elements

git-svn-id: https://netgen-mesher.svn.sourceforge.net/svnroot/netgen-mesher/netgen@664 38e36fca-e102-11dd-b6c5-65a6809f2f0c
Merge remote-tracking branch 'remotes/trunk'