src/poky:bitbake: fetch2/wget: consider downloadfilename when checking for upstream

latest_versionstring() currently looks at just the end of the URI when
guessing what the filename to look for is, but this doesn't work if the
URL filename is not simple.

For example, miniupnpd has a SRC_URI of:

  http://miniupnp.tuxfamily.org/files/download.php?file=${BP}.tar.gz;downloadfilename=${BP}.tar.gz

The filename component of this is "download.php", which causes the
heuristics in latest_versionstring() to exit early.

Instead, if the downloadfilename is set then use that, as it's often the
actual filename that we're after.

(Bitbake rev: 2d5f135e997d13fabda0ad266fd5c928ee33f487)

Signed-off-by: Ross Burton <ross.burtonarm.com>
Signed-off-by: Richard Purdie <richard.purdielinuxfoundation.org>

Author: rossburton