Bigger patch for (partial) tinylogin integration

- Made a new dir loginutils
- Moved all applets from pwd_grp to loginutils
- Added new applets su.c login.c to loginutils
- Made a new dir libpwdgrp
- Moved everything from pwd_grp/libpwd_grp there
- Added shadow.c to libpwdgrp
- Removed dir pwd_grp
- Added usage strings for login and su to usage.h
- Changed main Makefile to reflect the dir rearrangements
[Parts of this patch may overlap with my other two patches]

include/usage.h

@@ -978,6 +978,15 @@
 #define logger_example_usage \
 	"$ logger "hello"\n" 
 
+#define login_trivial_usage \
+	"[OPTION]... [username] [ENV=VAR ...]"
+#define login_full_usage \
+	"Begin a new session on the system\n\n" \
+	"Options:\n" \
+	"\t-f\tDo not authenticate (user already authenticated)\n" \
+	"\t-h\tName of the remote host for this login.\n" \
+	"\t-p\tPreserve environment."
+
 #define logname_trivial_usage \
 	""
 #define logname_full_usage \
@@ -1570,6 +1579,13 @@
 	"\n\t-g\t\tprint in stty-readable form" \
 	"\n\t[SETTING]\tsee manpage"
 
+#define su_trivial_usage \
+	"[OPTION]... [-] [username]"
+#define su_full_usage \
+	"Change user id or become root.\n" \
+	"Options:\n" \
+	"\t-p\tPreserve environment"
+
 #define swapoff_trivial_usage \
 	"[OPTION] [DEVICE]"
 #define swapoff_full_usage \