Closes [t:2624] Added toku_os_close() which retries on EINTR.  Closes [t:2621] Added toku_os_open(), toku_os_fopen(), toku_os_fdopen(), toku_os_fclose() and related override hooks  db_env_set_func_open(), db_env_set_func_fopen(), db_env_set_func_fdopen(), db_env_set_func_fclose(). Modified test program loader-cleanup-test to use new hooks to inject synthetic errors.  Marked some error cases in brtloader.c. with ###.

git-svn-id: file:///svn/toku/tokudb@20364 c7de825b-a66e-492c-adef-691d508d4ae1