Put back 'pgbuild.sh', which was removed accidentally.

Oops, I deleted it accidentally in commit 96beffb3c5. Put it back.

pgbuild.sh

@@ -0,0 +1,33 @@
+#!/bin/sh
+#
+#   Purpose of this script is to build and install postgres in a local directory
+# so that zenith intergation tests would find pg binaries and support files.
+#
+# ./pgbuild.sh would do following:
+#
+#   1) run out-of-source build of postgres in REPO_ROOT/tmp_install/build directory (I'm reusing
+#  tmp_install path here since it is already present in .gitignore)
+#
+#   2) installs postgres to REPO_ROOT/tmp_install/
+#
+
+# Halt immediately if any command fails
+set -e
+
+REPO_ROOT=$(dirname "$0")
+REPO_ROOT="`( cd \"$REPO_ROOT\" && pwd )`"
+
+# configure
+echo "Configuring postgres build"
+mkdir -p $REPO_ROOT/tmp_install/build
+cd $REPO_ROOT/tmp_install/build
+../../vendor/postgres/configure CFLAGS='-O0' --enable-debug --enable-cassert \
+    --enable-depend --with-libxml --prefix=/ > configure.log
+
+# compile
+echo "Compiling postgres"
+make -j8 -s
+export DESTDIR=$REPO_ROOT/tmp_install
+
+echo "Installing postgres to $DESTDIR"
+make install -s