Previously, a command like

   cabal install uHttpc

would silently auto-correct this to

   cabal install uhttpc

However, this is inconsistent as `build-depends` or `constraints`
are case-insensitive.

So with this patch,

   cabal install VULKAN uHttpc

result in the following error(s) instead:

   There is no package named 'VULKAN'. However, the following package names exist: 'Vulkan', 'vulkan'.

   There is no package named 'uHttpc'. However, the following package name exists: 'uhttpc'.