Greedy feature request: Support changing manifest

[Keno]

It often happens that I find a bug in a package that one of my packages depends on, so I dev it, but now I have the wrong package loaded. Often it's actually the same package as I already have loaded (because dev just gave me the same contents but as a git repo), but in a different place. It would be nice if Revise could switch over the module to the dev'ed copy.

[timholy]

Fixed in #217.

julia> Example.f()
ERROR: MethodError: no method matching f()
Stacktrace:
 [1] top-level scope at none:0

(v1) pkg> dev Example
[ Info: Path `/home/tim/.julia/dev/Example` exists and looks like the correct package, using existing path
 Resolving package versions...
  Updating `~/.julia/environments/v1/Project.toml`
  [7876af07] ↑ Example v0.5.1 ⇒ v0.5.1+ [`~/.julia/dev/Example`]
  Updating `~/.julia/environments/v1/Manifest.toml`
  [7876af07] ↑ Example v0.5.1 ⇒ v0.5.1+ [`~/.julia/dev/Example`]

julia> Example.f()
π = 3.1415926535897...

(v1) pkg> free Example
 Resolving package versions...
  Updating `~/.julia/environments/v1/Project.toml`
  [7876af07] ↓ Example v0.5.1+ [`~/.julia/dev/Example`] ⇒ v0.5.1
  Updating `~/.julia/environments/v1/Manifest.toml`
  [7876af07] ↓ Example v0.5.1+ [`~/.julia/dev/Example`] ⇒ v0.5.1

julia> Example.f()
ERROR: MethodError: no method matching f()
Stacktrace:
 [1] top-level scope at none:0

(v1) pkg> dev Example
[ Info: Path `/home/tim/.julia/dev/Example` exists and looks like the correct package, using existing path
 Resolving package versions...
  Updating `~/.julia/environments/v1/Project.toml`
  [7876af07] ↑ Example v0.5.1 ⇒ v0.5.1+ [`~/.julia/dev/Example`]
  Updating `~/.julia/environments/v1/Manifest.toml`
  [7876af07] ↑ Example v0.5.1 ⇒ v0.5.1+ [`~/.julia/dev/Example`]

julia> Example.f()
π = 3.1415926535897...

Prediction: you have some old packages lying around, installed prior to the days when added packages were checked out with read-only flags. Do a Pkg.gc() and then see if it works. You might have to forcibly remove and re-add some things.

[timholy]

Closing pending a MWE that illustrates a problem with the solution currently in place.