Call setreuid(euid, euid) in csc-chfn and csc-chsh on setup

This fixes an important bug in these utilities, in that
they didn't actually work for regular users.

bin/csc-chfn

@@ -74,6 +74,9 @@ def main():
 
     pwuid, pwnam = whoami()
 
+    euid = os.geteuid()
+    os.setreuid(euid, euid)
+
     gecos_params = {}
 
     try:

bin/csc-chsh

@@ -55,6 +55,9 @@ def main():
 
     pwuid, pwnam = whoami()
 
+    euid = os.geteuid()
+    os.setreuid(euid, euid)
+
     try:
         options, arguments = getopt.gnu_getopt(sys.argv[1:], 's:')
         new_shell = None