Update Maven GPG plugin from 1.4 to 1.5.

Just to keep up-to-date. Release notes: http://jira.codehaus.org/browse/MGPG/fixforversion/17635
Remove redundant field fCause
Merge pull request #836 from paulkrause88/patch-1

Remove redundant field fCause
Create AssumptionViolatedException in org.junit and deprecate the one in org.junit.internal

Allows developers to write code that handles assumption violations without depending on internal classes
Merge pull request #818 from dhasday/external-assumption-violated-exception

External version of AssumptionViolatedException
Merge pull request #1 from junit-team/master

Missing dependencies