Fix strong properties with mutable variants to be copy
Copy copied properties in -init
Remove existing header key before setting new one

This ensures that case of headers is preserved. NSMapTable reuses old keys that are equivalent
Use isolation queues to protect accounting collections
Add comments about use of isolation queues/write barriers
Merge pull request #13 from prachigauriar/umkmockurlprotocol-isolation-queues

Use isolation queues to protect accounting collections
Prep for 1.1.1 release
Merge pull request #14 from prachigauriar/dev

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