bugs when avoiding repeat compilation

When x10 file is older than oldest(cc,h,inc) it is not considered by the back end at all (X10CPPSourceClassResolver). This is also true if the x10 file is listed in the manifest, regardless of ages of files.

This means the list of output files may be complete for the following reasons

1) x10 file depends on native files generated from another X10 class that was not listed explicitly on the x10c++ commandline

2) x10 file depends on another native file that was provided using @NativeCPPCompilationUnit @NativeCPPInclude or @NativeCPPOutputFile within the x10 file in question

3) x10 file declares a struct and therefore generates an extra .struct_h file which is not known about before the backend runs.