Mapnik dep updates

[springmeyer]

Adds:

• icu 57.1 package
  • reduced .dat file size via https://ssl.icu-project.org/datacustom/)
  • fixed optimization flags
• boost_libregex_icu57 1.63.0 (built against icu 57)
• geos 3.6.1
• postgres 9.6.2
• libpq 9.6.2
• postgis 2.3.2
• libxml2 2.9.4

Fixes:

• optimization flags for gdal
• ldflags for gdal 2.1.3 package
• zlib system package unbound var on linux