support -search=path not relative to current dir

[v6cc]

now -search need full path, but only can found file relative to current dir, feel confused

hope full path can found file in other dir

A use case is I hope search current file

• if current file can found in relative dir, just open dir in defx, focus file, but not change dir
• if file not in current dir, change dir to new dir and focus

but now

Defx            -no-toggle -no-focus -search=`expand('%:p')      can't found other dir file;  
Defx `getcwd()` -no-toggle -no-focus -search=`expand('%:p')`     cause change dir when file relative to current dir

[Shougo]

I have added relative path support.

[Shougo]

Well, I have confused. It seems new feature.