fix out of tree build when using git src repo

fix out of tree build when using git src repo

The out of tree build failure only occurs when using git dev version.
It results from mismatch directory for textual data files.
It does not happen when using distributed tar ball because the textual
data files are distributed in the archive's data directory.

This patch will workaround the problem by uncompressing downloaded
textual data archive into src/data directory.
Note in this way we cannot do VPATH build when developing. Let's just
assume that use case is rare.