(CMake) customisable version/soversion

[rayglover-ibm]

In the CMake configuration, the libcaffe.so soname, derived from the CAFFE_TARGET_SOVERSION variable here, contains the 0-rc3 patch/revision information.

AFAIK this is against the general convention (described here and other places), and has caused me a few issues, e.g. with CMake (when creating the symlink-chain through cmake build . --target install) and Bazel (when including Caffe as a pre-built external project) both of which prefer the more canonical soname form: lib{name}.so.{number}.

This complicates the scenario when I want to maintain multiple versions of Caffe on the same machine, as shared libraries. Rather than changing the soname itself, I suggest the relevant variable is made customisable at the command line, which regardless I think is more generally useful.

[lukeyeager]

AFAIK this is against the general convention

This complicates the scenario when I want to maintain multiple versions of Caffe on the same machine, as shared libraries.

I totally agree. See discussion here for why the current versions were chosen:
#3311 (comment)

I support merging this PR as it simply allows users to choose their own versioning scheme. Afterwards, I'd still like to have a discussion about setting up a proper versioning scheme for mainstream Caffe.

[shelhamer]

I support merging this PR as it simply allows users to choose their own versioning scheme. Afterwards, I'd still like to have a discussion about setting up a proper versioning scheme for mainstream Caffe.

Sounds reasonable. Let's revisit this after the NIPS deadline 05/20. Merging for its clear use case.