Package names with dashes cause bad %files section

[Slavek Kabrda]

Trying pyp2rpm on devpi-common, I got files section with

%{python2_sitelib}/devpi-common

In these cases, pyp2rpm should replace dashes in package name by underscores for use in %files sections.

[Robert Kuska]

Return underscored name from package_to_path function, fixes #22

→ <<cset bf96960c4371>>

[Robert Kuska]

package_to_path function should return package (after all) with underscores, fixes #22

→ <<cset 7db699a0f3cd>>