Clean up lib path searching for Spatialite

Anything linking against SpatiaLite also needs to use Homebrew's SQLite so that
loadable extensions are enabled along with RTree indices.

This commit cleans up several formulae to use the specific `opt/sqlite/lib`
prefix rather than `HOMEBREW_PREFIX/lib` and also adds this searching to
`gdal`.

However, this hack is getting a little large. The best fix would probably be to
flag SQLite as `keg_only` so that lib path munging is handled automagically for
everything with a dependency tree that includes SQLite.

Formula/gdal.rb

@@ -210,10 +210,12 @@ class Gdal < Formula
   def install
     # Linking flags for SQLite are not added at a critical moment when the GDAL
     # library is being assembled. This causes the build to fail due to missing
-    # symbols.
+    # symbols. Also, ensure Homebrew SQLite is used so that Spatialite is
+    # functional.
     #
     # Fortunately, this can be remedied using LDFLAGS.
-    ENV.append 'LDFLAGS', '-lsqlite3'
+    sqlite = Formula.factory 'sqlite'
+    ENV.append 'LDFLAGS', "-L#{sqlite.opt_prefix}/lib -lsqlite3"
     # Needed by libdap.
     ENV.append 'CPPFLAGS', '-I/usr/include/libxml2' if complete?
 

Formula/librasterlite.rb

@@ -12,7 +12,8 @@ class Librasterlite < Formula
 
   def install
     # Ensure Homebrew SQLite libraries are found before the system SQLite
-    ENV.append 'LDFLAGS', "-L#{HOMEBREW_PREFIX}/lib"
+    sqlite = Formula.factory 'sqlite'
+    ENV.append 'LDFLAGS', "-L#{sqlite.opt_prefix}/lib"
     system "./configure", "--disable-dependency-tracking",
                           "--prefix=#{prefix}"
     system "make install"

Formula/libspatialite.rb

@@ -25,7 +25,8 @@ class Libspatialite < Formula
 
   def install
     # Ensure Homebrew's libsqlite is found before the system version.
-    ENV.append 'LDFLAGS', "-L#{HOMEBREW_PREFIX}/lib"
+    sqlite = Formula.factory 'sqlite'
+    ENV.append 'LDFLAGS', "-L#{sqlite.opt_prefix}/lib"
 
     args = %W[
       --disable-dependency-tracking

Formula/spatialite-tools.rb

@@ -19,7 +19,8 @@ class SpatialiteTools < Formula
     # See: https://github.com/mxcl/homebrew/issues/3328
     ENV.append 'LDFLAGS', '-liconv'
     # Ensure Homebrew SQLite is found before system SQLite.
-    ENV.append 'LDFLAGS', "-L#{HOMEBREW_PREFIX}/lib"
+    sqlite = Formula.factory 'sqlite'
+    ENV.append 'LDFLAGS', "-L#{sqlite.opt_prefix}/lib"
 
     system "./configure", "--disable-dependency-tracking",
                           "--prefix=#{prefix}"