package-id errors when ghc version is mismatched

[mgsloan]

Steps:

1. Compile ghc-mod with ghc 7.10.3

2. Use it with a project that uses ghc 7.10.2

Expected: Some error indicating that ghc-mod was compiled against the wrong ghc.

Actual: Get dependency satisfaction errors like

ghc-mod: <command line>: cannot satisfy -package-id hybrid-vectors-0.2-5d29072cf6121d18676f3e4e08bfac75: 
    hybrid-vectors-0.2-5d29072cf6121d18676f3e4e08bfac75 is unusable due to missing or recursive dependencies:
      base-4.8.1.0-4f7206fd964c629946bb89db72c80011 deepseq-1.4.1.1-8fb9688ae42216e388cee132aef3d148 primitive-0.6-f39f6bcba2f66e648d35c2c6a451ec07 vector-0.10.12.3-a4b33f1195787a40d0ade3cf6a172b0c
    (use -v for more information)

I suspect what's happening is that ghc-mod with 7.10.3 can use 7.10.2's package DBs. However, it uses the wrong global DB.

Suggested resolution: Check GHC version.

[DanielG]

Duplicate, see: #687 and #673