Fix configure error when determining id3lib version

Fix configure error when determining id3lib version

Error message:
  checking for library containing ID3Tag_Link... -lid3 -lz -lstdc++
  using shared id3lib
  checking for id3lib version... ./configure: line 16703: .: conftest.id3:
    file not found

Explanation:
The source command '.' in bash searches $PATH when given a file without a path.
So you need to use '. ./conftest.id3' to search in current directory.

Patch by Mike Frysinger taken from:
  http://sourceforge.net/p/grip/patches/152/