makefile.vc requires macro _INSTALLDIR

Environment:
- Windows Vista Pro German
- MS-VC++6
- Windows Server 2003 SP1 SDK (Release)

C:\test\tk8.5.4\win>nmake -f makefile.vc install TCLDIR=c:\test\tcl8.5.4 INSTALLDIR=c:\test\tcl854 _INSTALLDIR=c:\test\tcl854

Installs into c:\test\tcl854\..

I have no idea where the additional path component ".." comes from.
Anyway, after the install, the folders c:\test\lib etc. exists with the tk contents. The makefile fails while integrating the tcl helpfile into the tk one. The tcl helpfile is not found in the installation destination path.

A workaround is to specify also the variable "_INSTALLDIR", which is used in the makefile:

C:\test\tk8.5.4\win>nmake -f makefile.vc install TCLDIR=c:\test\tcl8.5.4 INSTALLDIR=c:\test\tcl854 _INSTALLDIR=c:\test\tcl854

Notes:
- This bug was not present in tcl8.5.3.
- To build the winhelp, the patches of the following bugs must be applied:
- TCL:1934200
- TK: 1934272