PEX wheel support fetches the wrong wheel variant (cp27m instead of cp27mu)

[apollo13]

When specifying the platform there does not seem to be a way to specify the abi tag. This results in

 msgpack_python-0.4.7-cp27-cp27m-manylinux1_x86_64.whl

getting pulled in instead of

 msgpack_python-0.4.7-cp27-cp27mu-manylinux1_x86_64.whl

which uses UCS4 instead of UCS2 and is basically what every linux distribution uses (according to https://github.com/pypa/manylinux)

[kwlzn]

this is a known issue for folks resolving directly against pypi, but it'd be good to provide a repro here to confirm this is fixed in the upcoming work.

[apollo13]

This can be used to repro:

pex msgpack-python==0.4.7 -o test.zip --platform=manylinux1_x86_64 --no-build --wheel
unzip -l test.zip|grep cp27mu

[kwlzn]

@apollo13 platform/impl/abi tags are now directly targetable as of pex 1.4.0:

[omerta ~]$ pex msgpack-python==0.4.7 -o /tmp/throwaway --platform=linux-x86_64-cp-27-mu --no-build
[omerta ~]$ unzip -l /tmp/throwaway | grep cp27mu | head -1
warning [/tmp/throwaway]:  25 extra bytes at beginning or within zipfile
  (attempting to process anyway)
     1385  05-15-2018 17:33   .deps/msgpack_python-0.4.7-cp27-cp27mu-manylinux1_x86_64.whl/msgpack/__init__.py

(also noting that manylinux support is intended to be implicit, so you needn't specify it exactly on the commandline - any linux platform will implicitly pickup manylinux wheels now)