[PD] restrict "find externals" to exact matches

[IOhannes m zmoelnig]

On 2/26/21 8:40 PM, Lucas Cordiviola wrote:
> We can document
[...]
> - https://github.com/pure-data/deken/issues/84#issuecomment-786533931

note that this doesn't yet work with Pd-vanilla, as it requires a (tiny) 
bit of changes on the Pd-core side.

there's a branch in the pure-data repository that has these changes 
(named "feature/dekenception" or somesuch), but not even a pull-requests.
this branch also requires the latest deken incorporated into Pd (for 
which there isn't a PR yet either).

i'm planning to do the deken PR later this week, but as i did a bit of 
code-refactoring, it would require some more testing. volunteers are 
welcome.