Fix installing into PREFIX.

mk/sys.mk

@@ -7,7 +7,10 @@ INSTALL?=		install
 RANLIB?=		ranlib
 SH=			/bin/sh
 
-PREFIX=			
+PREFIX?=	
+_UPREFIX_SH=		case "${PREFIX}" in "") echo /usr;; *) echo "${PREFIX}";; esac
+_UPREFIX!=		${_UPREFIX_SH}
+UPREFIX=		${_UPREFIX}$(shell ${_UPREFIX_SH})
 PKG_PREFIX=		/usr/local
 
 PICFLAG?=		-fPIC
@@ -15,18 +18,18 @@ PICFLAG?=		-fPIC
 BINDIR?=		${PREFIX}/sbin
 BINMODE?=		0755
 
-INCDIR?=		${PREFIX}/usr/include
+INCDIR?=		${UPREFIX}/include
 INCMODE?=		0444
 
 LIBNAME?=		lib
-LIBDIR?=		${PREFIX}/usr/${LIBNAME}
+LIBDIR?=		${UPREFIX}/${LIBNAME}
 LIBMODE?=		0444
 SHLIBDIR?=		${PREFIX}/${LIBNAME}
 
-MANDIR?=		${PREFIX}/usr/share/man/man
+MANDIR?=		${UPREFIX}/share/man/man
 MANMODE?=		0444
 
-DOCDIR?=		${PREFIX}/usr/share/doc
+DOCDIR?=		${UPREFIX}/share/doc
 DOCMODE?=		0644	
 
 CONFMODE?=		0644