BUILD: add an AIX 5.2 (and later) target.

It's always a real pain to build on AIX and I constantly lose my flags,
so let's store them once for all in the Makefile.
diff --git a/Makefile b/Makefile
index 2aeda2b..7cc1708 100644
--- a/Makefile
+++ b/Makefile
@@ -74,7 +74,7 @@
 # Use TARGET=<target_name> to optimize for a specifc target OS among the
 # following list (use the default "generic" if uncertain) :
 #    generic, linux22, linux24, linux24e, linux26, solaris,
-#    freebsd, openbsd, cygwin, custom
+#    freebsd, openbsd, cygwin, custom, aix52
 TARGET =
 
 #### TARGET CPU
@@ -256,6 +256,13 @@
   USE_KQUEUE     = implicit
   USE_TPROXY     = implicit
 else
+ifeq ($(TARGET),aix52)
+  # This is for AIX 5.2 and later
+  USE_POLL        = implicit
+  USE_LIBCRYPT    = implicit
+  TARGET_CFLAGS   = -D_MSGQSUPPORT
+  DEBUG_CFLAGS    =
+else
 ifeq ($(TARGET),cygwin)
   # This is for Cygwin
   # Cygwin adds IPv6 support only in version 1.7 (in beta right now). 
@@ -263,6 +270,7 @@
   USE_TPROXY = implicit
   TARGET_CFLAGS  = $(if $(filter 1.5.%, $(shell uname -r)), -DUSE_IPV6 -DAF_INET6=23 -DINET6_ADDRSTRLEN=46, )
 endif # cygwin
+endif # aix52
 endif # openbsd
 endif # freebsd
 endif # solaris
diff --git a/README b/README
index ca6312d..06187a6 100644
--- a/README
+++ b/README
@@ -29,6 +29,7 @@
   - solaris     for Solaris 8 or 10 (others untested)
   - freebsd     for FreeBSD 5 to 8.0 (others untested)
   - openbsd     for OpenBSD 3.1 to 4.6 (others untested)
+  - aix52       for AIX 5.2
   - cygwin      for Cygwin
   - generic     for any other OS.
   - custom      to manually adjust every setting
@@ -107,6 +108,8 @@
 AIX 5.3 is known to work with the generic target. However, for the binary to
 also run on 5.2 or earlier, you need to build with DEFINE="-D_MSGQSUPPORT",
 otherwise __fd_select() will be used while not being present in the libc.
+If you get build errors because of strange symbols or section mismatches,
+simply remove -g from DEBUG_CFLAGS.
 
 
 2) How to install it