Revision 1862071

Add apr_dir_pread(), a variant of apr_dir_read() which allows callers
to read a directory with constant memory consumption:

* include/apr_file_info.h: Add warning on memory consumption for
  apr_dir_read; declare apr_dir_pread.

* file_io/unix/dir.c (apr_dir_pread): Rename from apr_dir_read and
  take pool argument.  (apr_dir_read): Reimplement using it.

* file_io/win32/dir.c, file_io/os2/dir.c: Likewise, but untested.

* test/testdir.c (test_pread) [APR_POOL_DEBUG]: Add test case.