JULIA_DEPOT_PATH: expand empty path to default

This makes the behavior for JULIA_DEPOT_PATH expansion match that
of JULIA_LOAD_PATH expansion and allows one to manipulate the path
uncondionally with shell expressions like this:

    export JULIA_DEPOT_PATH="$JULIA_DEPOT_PATH:/system/depot"

It also changes JULIA_LOAD_PATH expansion to do user name expansion
just like JULIA_DEPOT_PATH does, bringing the two variables into
closer behavioral agreement.

base/initdefs.jl

@@ -43,14 +43,30 @@ isinteractive() = (is_interactive::Bool)
 
 const DEPOT_PATH = String[]
 
+function append_default_depot_path!(DEPOT_PATH)
+ path = joinpath(homedir(), ".julia")
+ path in DEPOT_PATH || push!(DEPOT_PATH, path)
+ path = abspath(Sys.BINDIR, "..", "local", "share", "julia")
+ path in DEPOT_PATH || push!(DEPOT_PATH, path)
+ path = abspath(Sys.BINDIR, "..", "share", "julia")
+ path in DEPOT_PATH || push!(DEPOT_PATH, path)
+end
+
 function init_depot_path()
+ empty!(DEPOT_PATH)
  if haskey(ENV, "JULIA_DEPOT_PATH")
- depots = split(ENV["JULIA_DEPOT_PATH"], Sys.iswindows() ? ';' : ':')
- append!(empty!(DEPOT_PATH), map(expanduser, depots))
+ str = ENV["JULIA_DEPOT_PATH"]
+ isempty(str) && return
+ for path in split(str, Sys.iswindows() ? ';' : ':')
+ if isempty(path)
+ append_default_depot_path!(DEPOT_PATH)
+ else
+ path = expanduser(path)
+ path in DEPOT_PATH || push!(DEPOT_PATH, path)
+ end
+ end
  else
- push!(empty!(DEPOT_PATH), joinpath(homedir(), ".julia"))
- push!(DEPOT_PATH, abspath(Sys.BINDIR, "..", "local", "share", "julia"))
- push!(DEPOT_PATH, abspath(Sys.BINDIR, "..", "share", "julia"))
+ append_default_depot_path!(DEPOT_PATH)
  end
 end
 
@@ -148,6 +164,7 @@ function parse_load_path(str::String)
  env = current_project()
  env === nothing && continue
  end
+ env = expanduser(env)
  env in envs || push!(envs, env)
  end
  end