Fix typos in locks in ws_string

Fixes accidental double-unlocks in several ws_string methods.
Merge pull request #290 from xVin/fix-ws_string-locks

Fix typos in locks in ws_string
Add logical.commands file
Add stubs for logical commands
Implement ws_builtin_cmd_lnot()
Add implementation for ws_builtin_cmd_land()
Add implementation for ws_builtin_cmd_lnand()
Add implementation for ws_builtin_cmd_lor()
Add implementation for ws_builtin_cmd_lnor()
Add implementation for ws_builtin_cmd_lxor()