[test] fix mingw test issues with \r\n

see http://perl514.cpanel.net/build/builders/parrot-mingw32/builds/21/steps/shell_2/logs/stdio
[test] fixup mingw fixes
[cage] add const to env api STRING args

and fix 2 uninitialized vars
[cage] fix instances of -Wshadow

fix all instances of warning: declaration shadows a local variable
tested with latest clang++
[frontend]: activate -?/--help for pbc_merge

also some cage: comment removed variable, fix -Wshadow