Fix for Issue #6: "Merge PDF fails in alfresco share community edition"

 [The issue](https://github.com/ntmcminn/alfresco-pdf-toolkit/issues/6) was caused by a NullPointerException being thrown from PDFActionFormFilter.

The commits in this pull request include an integration test demonstrating the issue and a fix for the issue.

There are also two commits (44e63f2 and 213391b) that alter the build to target Alfresco Community 4.2.f and remove PDFConvertToArchivableActionExecuter which is only supported in Alfresco Enterprise. If this pull request is merged these two commits should be omitted to maintain all the enterprise-only features.