Revision of mkdist/CMakeLists for "overlapping" Deb package installations

[willend]

Prior to McCode 3.5.1

In McStas 3.4 (and McXtrace 3.2 etc.) and earlier on Deb class systems, installations would go to the installation hierarchy /usr/share/mcstas/, e.g. with location /usr/share/mcstas/3.4/, including installation binaries under /usr/share/mcstas/3.4/bin, symlinked into /usr/bin.

At the same time, package versioning was always v. 1.0, with package names containing the "McStas version", i.e.:

ii  mcstas-3.4                                         1.0          amd64        mcstas built using CMake
ii  mcstas-3.4.26                                      1.0          amd64        mcstas built using CMake
ii  mcstas-3.4.47                                      1.0          amd64        mcstas built using CMake
ii  mcstas-3.4.50                                      1.0          amd64        mcstas built using CMake
ii  mcstas-3.4.51                                      1.0          amd64        mcstas built using CMake
rc  mcstas-3.4.55                                      1.0          amd64        mcstas built using CMake
rc  mcstas-3.4.56                                      1.0          amd64        mcstas built using CMake
rc  mcstas-3.4.68                                      1.0          amd64        mcstas built using CMake
ii  mcstas-3.5.1                                       1.0          amd64        mcstas built using CMake

3.5.1 and later

All together, this means that with the new "standard location" there can only be one "global" McStas version installed:

• binaries go to /usr/bin
• "resources" go to /usr/share/mcstas/resoources
• "tools" go to /usr/share/mcstas/tools
  and so forth.

This unfortunately means that with 3.5.1 installed on a system, requesting 3.5.12 to be installed will mean a package conflict:

 dpkg: error processing archive mcstas-3.5.12-deb64.deb (--install):
 trying to overwrite '/usr/bin/mcstas', which is also in package mcstas-3.5.1 1.0
dpkg-deb: error: paste subprocess was killed by signal (Broken pipe)
Selecting previously unselected package mcstas-clustertools-3.5.12.
Preparing to unpack mcstas-clusterscripts-3.5.12-deb64.deb ...
Unpacking mcstas-clustertools-3.5.12 (3.5.12) ...
Selecting previously unselected package mcstas-comps-3.5.12.
Preparing to unpack mcstas-comps-3.5.12-deb64.deb ...

What to do - long term and short term

Once we have official Debian packages fully in place this should all be handled automatically, however in the interim we probably still need to update the CMake tooling (and mkdist?) to

• Implement package names without the version tag
• Use the version tag for the CPack packaging
• Implement use of CPACK_DEBIAN_PACKAGE_REPLACES to let a new package replace any existing, older, installed package.