R1:3544620209cf

Parse unusual Subversion protocol frames which contain extra whitespace

Summary:
Fixes T13140. See PHI660.

Recent versions of Subversion can send a `(get-file true false false )` protocol frame with extra space between "false" and "false". This is allowed by the protocol spec, but never normally happens, and we do not parse it correctly.

Instead, parse it correctly.

Test Plan:
- Added unit tests.
- Ran `svn proplist svn+ssh://.../diffusion/X/file.c` under SVN 1.10 before and after the change.