* [core]: prefix DB functions with DB

relax on Windows profile list test

fix many compiler warnings on MinGW
* [core]: fix compile warnings about wrong argument types

... on MinGW
* [yajl]: fix redefinition warning of math types on MinGW
* [oPNG]: fix compiler warning on MinGW
* [exmpl]: fix compiler warning for wrong formatter

... on MinGW
* [core]: remove double definition of dlopen
* [core]: remove define stat _stat

fix variable names for posix builds
* [oPNG]: compile again with libpng12

... by reverting #00b1e188
* [core]: rename missed symbol from recent DB prefixing

... #9e1e33c0