[Feature request] Maintainer script validation

[absidue]

Preamble
When Procursus switched the default shell from bash to dash, numerous packages failed to install and uninstall. This was due to the maintainer scripts in those packages being created with the assumptions that the default shell would be bash and that /bin/sh would be symlinked to bash.

Feature request
To help reduce future issues, I propose having some validation of the maintainer scripts in the DEB packaging in Theos. The most basic validation could include a check for a shebang and possibly a check for common bashisms such as if [[ in scripts with a #!/bin/sh shebang.

[L1ghtmann]

May be worth looking into a pre-existing tool/script (e.g., checkbashisms) to run checks before dm.pl runs.