Add DESTDIR support

From: David Rothenberger <daveroth@acm.org>


---
 SConstruct |   12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/SConstruct b/SConstruct
index dc54354..8703247 100644
--- a/SConstruct
+++ b/SConstruct
@@ -112,6 +112,9 @@ opts.AddVariables(
                   None),
   RawListVariable('CPPFLAGS', "Extra flags for the C preprocessor "
                   "(space separated)", None), 
+  PathVariable('DESTDIR', 'Directory to install under',
+               '',
+               PathVariable.PathAccept),
   )
 
 if sys.platform == 'win32':
@@ -184,6 +187,7 @@ apr = str(env['APR'])
 apu = str(env['APU'])
 zlib = str(env['ZLIB'])
 gssapi = env.get('GSSAPI', None)
+destdir = str(env.get('DESTDIR', ''))
 
 if gssapi and os.path.isdir(gssapi):
   krb5_config = os.path.join(gssapi, 'bin', 'krb5-config')
@@ -397,8 +401,8 @@ if CALLOUT_OKAY:
 
 # INSTALLATION STUFF
 
-install_static = env.Install(libdir, lib_static)
-install_shared = env.InstallVersionedLib(libdir, lib_shared)
+install_static = env.Install(destdir + libdir, lib_static)
+install_shared = env.InstallVersionedLib(destdir + libdir, lib_shared)
 
 if sys.platform == 'darwin':
   # If --install-sandbox=<path> is specified, install_shared_path will point
@@ -415,8 +419,8 @@ if sys.platform == 'darwin':
 
 env.Alias('install-lib', [install_static, install_shared,
                           ])
-env.Alias('install-inc', env.Install(incdir, HEADER_FILES))
-env.Alias('install-pc', env.Install(os.path.join(libdir, 'pkgconfig'),
+env.Alias('install-inc', env.Install(destdir + incdir, HEADER_FILES))
+env.Alias('install-pc', env.Install(os.path.join(destdir + libdir, 'pkgconfig'),
                                     pkgconfig))
 env.Alias('install', ['install-lib', 'install-inc', 'install-pc', ])