Merge branch 'hotfix/67' into develop

Forward port #67
Merge branch 'feature/69' into develop

Forward port #69
Merge branch 'hotfix/65' into develop

Forward port #65
Merge branch 'hotfix/75' into develop

Forward port #75
Merge pull request #76 in develop
Merge pull request #83 in develop
ZendDiagnostics DiskFree Test coverage.
DiskFree test class, tests & doc section.
Merge branch 'develop'