Found out how to create patches without Eclipse plugins: http://ariejan.net/2007/07/03/how-to-create-and-apply-a-patch-with-subversion/
What I basically have to do is, after downloading the latest revision using:
svn co http://svn.apache.org/repos/asf/ant/core/trunk/ ant-core
and editing my files in Eclipse, I have to open a terminal window and type in:
svn diff > ~/fix_ugly_bug.diff
The diff extension allows text editors (like Notepad++ and possibly gedit) to recognize the language and use syntax highlighting. However, I’ve also seen patches in the Ant Bugzilla which were diff files with a .patch extension. (See previous post) The original post can be found here: https://anterence.blogspot.com/2010/06/patches-in-svn.html