State-mutating GET methods in webapi.

[nejucomo]

Based on the documentation for the webapi, GET operations should not modify state. However, a request to:

GET /operations/$HANDLE?retain-for=$AMOUNT

-and:

GET /operations/$HANDLE?release-after-complete=$BOOL

-both alter the state associated with an in-progress operation. Should these parameters be altered by a POST instead?

If not, the documentation should explicitly mention this as an exception.