lib-php: rename find_user_plan to find_user_plan_file
lib-php: add functions to read plan from file and LDAP
ui-finger: use read_user_plan()
config: document LDAP options
lib-php: fix inverted condition in read_user_plan_ldap
Merge branch 'plan-ldap'

Allow the .plan file to be read from LDAP, which makes more sense in
distributed environments (like the ones rwho normally runs on). I'm
still not sure what will happen to the 'plan-edit' branch, and whether I
should add the editing commands to 'cn' instead.