add two tests for compiling XPath expression 
fix the issue where an XPath contains an undefined function and the error is only exposed during evaluation. Should check the result pointer


github.com/moovweb/manhattan/issues/1070
a bad xpath at runtime returns an empty array
should free the memory in test
a test that causes memory leaks in libxml
add a string function to return the xpath itself
evaluation of an xpath could return error. pop it up to Search
update test cases.
fix memory leak and crash
Merge branch 'master' into release_4.0
add SearchByDeadline
add SearchByDeadline
go fmt
Free XPath explicitly
Free XPath explicitly
the regex objects cannot be shared and must be created dynamically
merge
remove unused global var
remove unused global var
Merge branch 'release_4.0'