* new/virtual-target.jam
(subvariant-dg.implicit-includes): New method.
(subvariant-dg.__init__): Check for <implcit-dependency>, not all
dependency features.
* new/builtin.jam
(compile-action.adjust-properties): Call 'implicit-includes'.
[SVN r20174]
targets are specified as sources, not only as dependency properties.
* new/virtual-target.jam (subvariant-dg): Note which sources
are roots of dependency grapgs and record those graphs.
[SVN r16095]
For example, this would allow compilers to add generated headers into include
path.
* virtual-target.jam (action.adjust-properties): New rule.
(clone-action-template): Don't slice cloned object.
* generators.jam (generator.action-class): New rule, to allow
overriding action class on per-generator basis.
* builtin.jam (compile-action): New class.
(C-compiling-generator): New class.
* gcc.jam: Use C-compiling-generator for gcc. Honor includes.
[SVN r15618]
