apr: updated to 1.7.3

Changes for APR 1.7.3

*) apr-1-config: Fix crosscompiling detection in apr-1-config.

*) configure: Add --enable-sysv-shm to use SysV shared memory (shmget) if
  available.

*) apr_socket_sendfile: Use WSAIoctl() to get TransmitFile function
  pointer on Windows.

*) apr_dir_read: Do not request short file names on Windows 7
  and later.

*) apr_file_gets: Optimize for buffered files on Windows.

*) Fix a deadlock when writing to locked files opened with APR_FOPEN_APPEND
  on Windows.

*) Don't seek to the end when opening files with APR_FOPEN_APPEND on Windows.

*) apr_file_write: Optimize large writes to buffered files on Windows.

*) apr_file_write: Optimize large reads from buffered files on Windows.

(adam)