Fix #1032

Fix #1034

dpkg-gencontrol can be called with -v flag which set binary package's
version separated from source version. When this happen, the Source
field will contain version number in addition to source package name.
This tripped Aptly's dbgsym restriction, which check for exact source
package name, which in turn prevents the dbgsym & the whole .changes
file from being imported.

From the git history, it seems like this condition is a leftover from
when Aptly filter dbgsym packages using "*-dbgsym". So, I decided to
remove it. A test case has been added to prevent regression.

We use go modules now.

Also, update "pkg/errors" library.