Changed target name of postgres to postgresql

The target for building the app and for building the postgres binaries
were both named "postgres". XCode gets confused when two targets have
the same name. Once you build one of them, the other disappears from
the target popup menu. If this problem affects you, delete the
xcuserdata subdirectory within the project file. This commit should
prevent the problem from occurring in the future.
Use our own OpenSSL build

Apple has deprecated linking to the system provided OpenSSL libraries. In this commit, I added a target that downloads and builds our own copy of OpenSSL. I've also updated the postgresql build script to compile and link against our version of OpenSSL. Additionally, I updated the dylib-target so that it also fixes all the OpenSSL-related paths.
Updated plv8 target to GYP-based build system

The v8 project has moved from the SCons build system to GYP. I've updated the plv8 target to now build v8 using the new build system. Additionally, I've added a variable in the build settings to define which version of v8 to use.