tar and non-writable files in srcdir

[Ralf Wildenhues]

While extracting libtool-2.1a.tar.bz2 (tarball of CVS HEAD) over an
already present source tree on Solaris:
| ..
| tar: libtool-2.1a/config/ltmain.sh: Could not create file: Permission denied
| ..
| tar: libtool-2.1a/m4/ltversion.m4: Could not create file: Permission denied
| ..

Should we avoid putting non-writeable files in the source tree because
of this?  Why are we making them non-writeable in the first place?

Regards,
Ralf