Allows custom serializable const class/struct instances. Fixes #878

Serializer ignores custom serialization methods of const instances.
Reason is `isCustomSerializable!(const(T))` == `false`.
Wrapping email address inside angle brackets.

Both smtp.zoho.com and smtp.gmail.com refuse to go through if an email address is not wrapped inside angle brackets...
The problem hits when sending mail through userman. Should it be fixed in userman or in vibe, your call. 

thx.
add skip method to mongodb cursor
Merge pull request #888 from MartinNowak/mongodbCursorSkip

add skip method to mongodb cursor
Merge pull request #887 from ohenley/patch-2

Wrapping email address inside angle brackets.
Merge pull request #879 from japplegame/patch-1

Allows custom serializable const class/struct instances. Fixes #878
- fix RedisReply for set returning simple string result
- add tests for the broken cases
Merge pull request #890 from Extrawurst/master

fix RedisReply for redis SET returning simple string result
Avoid sleep(0.msecs) call (triggers an assertion).
fix redis Locking idiom (lua script uses KEYS, but those were not given in the call of the script)
Merge branch 'master' of https://github.com/rejectedsoftware/vibe.d
Merge pull request #891 from Extrawurst/master

fix redis Locking idiom and added tests
Fix condition for internal assertion.
Make sleep(0.seconds) a no-op instead of throwing an AssertError.
Merge branch 'master' of https://github.com/rejectedsoftware/vibe.d