Fix go-swagger/go-swagger#1796 (circular $ref with cycle in remote)

[fredbi]

• contributes Recursive model errors during flattening stage of generate server go-swagger/go-swagger#1796
• contributes One spec in multiple files (data types logic override) - error of generating go-swagger/go-swagger#1767
• contributes Are external references supported? go-swagger/go-swagger#1774

Signed-off-by: Frederic BIDON fredbi@yahoo.com

[codecov]

Codecov Report

Merging #40 into master will decrease coverage by 0.05%.
The diff coverage is 84.21%.

@@            Coverage Diff             @@
##           master      #40      +/-   ##
==========================================
- Coverage   92.81%   92.76%   -0.06%     
==========================================
  Files           7        7              
  Lines        1643     1659      +16     
==========================================
+ Hits         1525     1539      +14     
- Misses         72       73       +1     
- Partials       46       47       +1

Impacted Files	Coverage Δ
flatten.go	85.9% <84.21%> (+0.03%)	⬆️

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[fredbi]

Strange build failure with golangci:

ErrorFailed to load program with go/packages: go [list -e -json -compiled -test=true -export=false -deps=true -- ./...]: exit status 1: go build github.com/go-openapi/jsonpointer: no Go files in
go build github.com/go-openapi/spec: no Go files in
go build github.com/go-openapi/strfmt: no Go files in
go build github.com/go-openapi/swag: no Go files in
"

[kstedman9]

@fredbi I pulled your changes locally and rebuilt my complete swagger. It seems to fix the issues I was having with the flattening issue. I will do more work on it this weekend to verify it.

[fredbi]

Reported golangci failure: golangci/golangci#25

[fredbi]

Thanks @kstedman9! You also have a WIP PR on go-swagger which onboards this change and tests some similar issues.