Try to fix incorrect method invalidation in the serializer

[yuyichao]

From #22355 (comment). No feedback in 4hrs so I decided to put it here and not hijack #22355 any longer....

[yuyichao]

Note that this is intentionally against #22340. @vtjnash

[vtjnash]

Sorry, this has sent me down quite a rabbit hole for the past four hours. So far I've got:

commit 1b23eee3e3745ac69f32f75446dd11f7fbaeb0e3
Author: Jameson Nash <[email protected]>
Date:   Tue Jun 13 18:34:03 2017 -0400

    fixup!
    
    make precompile edges smarter
    reverts 8dab956ea30793621b0842ba13223d61b3d0490e and 11a984bb301e14d6fbd572cb63eea494cf6ab733
    who needed them anyways
...
< new >
commit 11a984bb301e14d6fbd572cb63eea494cf6ab733
Author: Jameson Nash <[email protected]>
Date:   Mon Jun 12 14:05:20 2017 -0400

    enable GC sooner when loading precompiled modules
    
    part of #20671
...
< on master >
commit 8dab956ea30793621b0842ba13223d61b3d0490e
Author: Jameson Nash <[email protected]>
Date:   Wed Jun 7 13:10:00 2017 -0400

    incremental serialize: restore recache order back to original
    
    the commit fix for #265 reshuffled this order, but that was wrong
    the correctness of jl_recache_other has since been fixed,
    permitting this to go back to the correct original order
    
    fix #22171

and also got a slightly better idea of what a backedge might be. :)