operations: force user to set the caller when collecting is done.

In order to save users from debugging deadlocks, force them to declare the
caller when using collect(), directly or indirectly. Does not influence send()

Signed-off-by: Peter Soetens <peter@thesourceworks.com>
scripting: allow parsing of keywords at the end of a parse string.

The Taskbrowser refused to parse 'foo=true' because keywords implicitly assumed something
was after it. Users had to write 'foo=1' to work around this. Now we allow to parse a keyword
at the end of a line or end of parse string.

Signed-off-by: Peter Soetens <peter@thesourceworks.com>