fix(makefile): honor DESTDIR and PREFIX for tic (terminfo generation)

[actionless]

fixes #78

$ make PREFIX=/usr DESTDIR=./pkgdir/ install
<...>

$ tree -a pkgdir/
pkgdir/
└── usr
    ├── bin
    │   └── xst
    └── share
        ├── man
        │   └── man1
        │       └── xst.1
        └── terminfo
            └── x
                ├── xst
                ├── xst-256color
                ├── xst-bs
                ├── xst-bs-256color
                ├── xst-meta
                ├── xst-meta-256color
                └── xst-mono