duplicate name in manifest warnings

[emaldona]

For https://pagure.io/jss/issue/18

[cipherboy]

I have:

• Tested and built this PR locally.
• Verified that the issue is valid.

  [jss@localhost ~]$ grep 'WARNING:' ./jss_master*
  ./jss_master_build.stderr:WARNING: Duplicate name in Manifest: Name.
  ./jss_master_build.stderr:WARNING: Duplicate name in Manifest: Specification-Title.
  ./jss_master_build.stderr:WARNING: Duplicate name in Manifest: Specification-Version.
  ./jss_master_build.stderr:WARNING: Duplicate name in Manifest: Specification-Vendor.
  ./jss_master_build.stderr:WARNING: Duplicate name in Manifest: Implementation-Title.
  ./jss_master_build.stderr:WARNING: Duplicate name in Manifest: Implementation-Version.
  ./jss_master_build.stderr:WARNING: Duplicate name in Manifest: Implementation-Vendor.
  ```
  

• Verified that it removes the warning from the referenced issue.

  [jss@localhost ~]$ grep 'WARNING:' ./jss_branch*
  [jss@localhost ~]$ 
  

Thanks for the PR @emaldona! :)

[cipherboy]

For future reference (AI: @cipherboy):

In the code, it isn't obvious but the variable $append is local and static. The local part is fixed by #30, but removing the conditional would be nice. In particular, it seems like the append behavior isn't desired.