data-lens is not a dep of idris

lens is, but that isn't available in the binary repos of the old version
of Ubuntu Travis-CI runs.
Set the handles used for --client to use UTF-8

Previously they were binary-mode, so they used char8 “encoding”, taking
codepoint values modulo 256, leading to cryptic identifier mangling errors
when using idris-vim.
Fix typo in Idris network C code
add system to Effects.System as is
add system to Effects/System neweffects
Predicates for Prelude Strings
Merge pull request #1229 from LeifW/travis_deps

Don't bother installing data-lens
Merge pull request #1334 from Melvar/fix-ipc-enc

Set the handles used for --client to use UTF-8
Merge pull request #1336 from Heather/system

add system to Effects.System as is
Merge pull request #1345 from bmsherman/idrisNetFix

Fix typo in Idris network C code
Merge pull request #1352 from Heather/string

Predicates for Prelude Strings