install and upgrade doc updates for 2.4.0

[Galen Charlton]

Several patches implementing various updates to the install and upgrade documentation are available in the collab/gmcharlt/install_upgrade_instructions_for_2_4 branch of the working/Evergreen repository:

http://git.evergreen-ils.org/?p=working/Evergreen.git;a=shortlog;h=refs/heads/collab/gmcharlt/install_upgrade_instructions_for_2_4

    - specify minimum supported PostgreSQL version as 9.1
    - specify minimum supported OpenSRF version as 2.2.0
    - update schema upgrade instructions and miscellaneous
      references to 2.3
    - Increase chances that somebody following the instructions
      precisely doesn't run into a problem during the configure step.

[Mike Rylander (mrylander)]

Merged to master and 2.4. Thanks, Galen!