cmd/deps: show deps for head spec with --HEAD

[EricFromCanada]

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---

Just adding the option is all it needed to work. Not sure if it should warn when a formula has no head spec. Also includes a few man page fixes.

$ brew deps --include-build --tree --annotate coreutils
coreutils
└── gmp 

$ brew deps --include-build --tree --annotate --HEAD coreutils
coreutils
├── gmp 
├── autoconf  [build]
│   └── m4 
├── automake  [build]
│   └── autoconf 
│       └── m4 
├── bison  [build]
├── gettext  [build]
├── texinfo  [build]
├── wget  [build]
│   ├── libidn2 
│   │   ├── libunistring 
│   │   ├── gettext 
│   │   └── pkg-config  [build]
│   ├── openssl@3 
│   │   └── ca-certificates 
│   └── pkg-config  [build]
└── xz  [build]

[MikeMcQuaid]

Makes sense to me!

[EricFromCanada]

Added a warning if one or more of the named args has no head spec:

$ brew deps --include-build --annotate --HEAD --tree zssh zsh zoro 
Warning: No head spec for zoro or zssh, using stable spec instead
zoro
└── go  [build]

zsh
├── ncurses 
│   └── pkg-config  [build]
├── pcre 
└── autoconf  [build]
    └── m4 

zssh
├── lrzsz 
├── autoconf  [build]
│   └── m4 
├── automake  [build]
│   └── autoconf 
│       └── m4 
└── libtool  [build]
    └── m4 

[MikeMcQuaid]

Thanks again @EricFromCanada!