Bugs in apr_file_trunc

[Julian Foad]

It came to my notice that apr_file_trunc() has some bugs which have been 
worked around in Subversion.

Please see svn_io_file_trunc() in subversion/libsvn_subr/io.c :
http://svn.apache.org/viewvc/subversion/trunk/subversion/libsvn_subr/io.c?view=markup&pathrev=1759116#l4065

r1240752 added a work-around
r1759116 added a further work-around, and a test

Might anyone care to investigate transferring these fixes and tests for 
them into APR?

- Julian