bugfix: race in sync2.BoundedRWLock

There's a race in the BoundedRWLock implementation which lets readers to
sneak through while a writer is holding the lock.

Example race:
 * Writer A calls `WUnlock()` and wakes up a whole bunch of readers inside
   `processQueue()` and releases `rw.control`.
 * Writer B arrives right before any of the readers could acquire the `rw.control` lock.
   Writer B thinks there are no readers and `rw.nextWriter == nil`. So it thinks it has
   an exclusive lock.
 * Finally the readers actually wake up, acquire `rw.control`, increment the `readers` counter.
   Now you've both readers and writer holding the lock at the same time.

Fix:

Whenever a reader is woken up, we also increment `rw.readers` counter immediately. This prevents
a writer from racing with the readers. Readers decrement the counter when they unlock as before.
Document the set interface
Add thread-safety comment
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Merge pull request #65 from 4578395263256/fix_test

Fix test TestConnectTimeout in net2/http2/simple_pool_test
Unittests for sync2.BoundedRWLock
Merge pull request #63 from mallipeddi/rwlock-fix

bugfix: race in sync2.BoundedRWLock
Switch to explicit enum sequence for serialization part
Merge pull request #66 from rajatgoel/master

Switch to explicit enum sequence for serialization part
Merge pull request #64 from teisenbe2/document_set

Document the set interface
fix time sql serialization.
go fmt
Merge pull request #68 from PatrickDropbox/sql-time

Fix time sql literal serialization