Introduce svn_io_file_putc() and svn_io_file_read_full2() for reduced
I/O call and result handling overhead. Use the latter wherever suitable
and both in APR streams.

Merged revisions from /branches/performance:
985487, 985488, 985497, 985493, 986465, 986491, 986517, 998012, 1029062


git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/integrate-io-improvements@1068684 13f79535-47bb-0310-9956-ffa450edef68
8 files changed