KWSys SystemInformation: Check for _SC_AIX_REALMEM before using it

Add a check for supported flag when querying for system memory on
AIX 5.1.
CMake Nightly Date Stamp
Merge branch 'doc-index-xrefs' into release
Merge branch 'doc-CMAKE_INSTALL_PREFIX-link-GNUInstallDirs' into release
Merge branch 'kwsys-SystemInformation-AIX-_SC_AIX_REALMEM' into release
Merge branch 'emacs-mode-underscore-in-symbol' into release
Merge topic 'emacs-mode-underscore-in-symbol'

cb80e513 Help: Add 3.1 release note Emacs mode update
30f14aeb cmake-mode.el: syntax of '_' should be treated as symbol
Merge topic 'doc-CMAKE_INSTALL_PREFIX-link-GNUInstallDirs'

00d4cdc9 Help: Link to GNUInstallDirs from CMAKE_INSTALL_PREFIX (#15246)
Merge topic 'doc-index-xrefs'

7ca9a459 Utilities/Sphinx: Add index entries for cross-references
Merge topic 'update-kwsys'

75009e4b Merge branch 'upstream-kwsys' into update-kwsys
35ecc355 KWSys 2014-11-12 (5843f590)
Merge topic 'fix-vs12-GetVersionEx-warning'

3a6c3599 Suppress deprecation warnings for GetVersionEx
Merge topic 'update-curl'

3dd26463 curl: Disable warnings to avoid changing 3rd party code
Merge branch 'master' into next
Merge topic 'kwsys-SystemInformation-AIX-_SC_AIX_REALMEM' into next

a234bcaf KWSys SystemInformation: Check for _SC_AIX_REALMEM before using it
Merge topic 'kwsys-SystemInformation-AIX-_SC_AIX_REALMEM'

a234bcaf KWSys SystemInformation: Check for _SC_AIX_REALMEM before using it
Merge branch 'master' into next
Merge branch 'release'
Merge branch 'master' into next