path_open all flags support

[pmp-p]

it seems path_open does not allocate fd when passed OFLAGS_CREAT, does not handle OFLAGS_EXCL
and maybe does not return all possible values in all posible cases ( ERRNO_EXIST / ERRNO_NOTDIR )

[konsumer]

Notes from discord:

• the fd is not allocated when creating
• it should test for file, then if file is not there, test for valid parent and rights to create in it
• leads to fopen with mode w/w+ failing right now
• needs logic here