Conditional OpExecutor selection

[Aklakan]

Some property functions do not work as expected when reordered, because they need input passed to them. Currently reordering is globally disabled which sometimes gives unacceptable long runtimes. Resolution of this issue should involve:

• A heuristic to automatically choose reordering (e.g. default is enabled, but use of property functions in a black list disable it)
• An explicit option to set the reordering mode (on/off/auto)

For example, fs:find requires ?path to be bound in order to yield results.

foo a ?path .
?path fs:find ?file

[Aklakan]

• Triple pattern reordering is now auto-disabled for every query that uses the SERVICE keyword and/or a user defined property function
• An explicit switch does not seem to be necessary; if needed this issue can be reopened.