5c613aadd64453c75cb2373c6fcc1326c3cf0b7a lint: Add linter for circular dependencies (Ben Woosley)
Pull request description:
Protects against added circular depencies, makes it explicit in the
code when circular dependencies have been removed.
Modeled after EXPECTED_BOOST_INCLUDES in lint-includes.sh
Example output:
```
$ test/lint/lint-circular-dependencies.sh
A new circular dependency in the form of "qt/paymentserver -> qt/walletmodel -> qt/paymentserver" appears to have been introduced.
$ echo $?
1
$ test/lint/lint-circular-dependencies.sh
Good job! The circular dependency "Fake" is no longer present.
Please remove it from EXPECTED_CIRCULAR_DEPENDENCIES in test/lint/lint-circular-dependencies.sh
to make sure this circular dependency is not accidentally reintroduced.
$ echo $?
1
$ test/lint/lint-circular-dependencies.sh
$ echo $?
0
```
Tree-SHA512: 4519434de29f6d50859daed1480e531c01c1cdbc3f0a5f093251daf62ae2b5b9073fb274b86f541a985e06837aa1165b76558c5f35fb51a759d72e83f1b61e44
