Switch the match, skiphigh and skiplow types from uint32_t to size_t,
they're key lengths.
Rewrite the read/write loops to handle short returns, POSIX allows short
returns, and Linux splits really large read/writes into multiple chunks.

Change __wt_read to take a size_t as the byte length instead of a uint32_t.
Finish renaming test_util05 -> test_verify.
Fix a bug I just introduced, pread has to handle EOF as an error.