Issue 1:
I have installed a number of modules system-wide under /usr/share/julia/environments/v1.0 using a Linux distribution package https://aur.archlinux.org/packages/julia-ijulia/

With Julia 1.0.2 these packages are detected and loaded, e.g.:

$ strace -f -estat julia
...
julia> using IJulia
[pid 30509] stat("/home/jonathon/.julia/environments/v1.0", 0x7ffdf6e551e0) = -1 ENOENT (No such file or directory)
[pid 30509] stat("/usr/local/share/julia/environments/v1.0", 0x7ffdf6e551e0) = -1 ENOENT (No such file or directory)
[pid 30509] stat("/usr/share/julia/environments/v1.0", {st_mode=S_IFDIR|0755, st_size=242, ...}) = 0
[pid 30509] stat("/usr/share/julia/environments/v1.0/JuliaProject.toml", 0x7ffdf6e551e0) = -1 ENOENT (No such file or directory)
[pid 30509] stat("/usr/share/julia/environments/v1.0/Project.toml", 0x7ffdf6e551e0) = -1 ENOENT (No such file or directory)
[pid 30509] stat("/usr/share/julia/environments/v1.0", {st_mode=S_IFDIR|0755, st_size=242, ...}) = 0
[pid 30509] stat("/usr/share/julia/environments/v1.0/JuliaProject.toml", 0x7ffdf6e55340) = -1 ENOENT (No such file or directory)
[pid 30509] stat("/usr/share/julia/environments/v1.0/Project.toml", 0x7ffdf6e55340) = -1 ENOENT (No such file or directory)
[pid 30509] stat("/usr/share/julia/environments/v1.0/IJulia.jl", 0x7ffdf6e55340) = -1 ENOENT (No such file or directory)
[pid 30509] stat("/usr/share/julia/environments/v1.0/IJulia/src/IJulia.jl", {st_mode=S_IFREG|0644, st_size=12461, ...}) = 0
...

Note that it looks under the path /usr/share/julia/environments/v1.0/IJulia/src/IJulia.jl.

With 1.0.3 this fails:

julia> using IJulia
[pid 17444] stat("/home/jonathon/.julia/environments/v1.0", 0x7ffe0d5fde00) = -1 ENOENT (No such file or directory)
[pid 17444] stat("/usr/local/share/julia/environments/v1.0", 0x7ffe0d5fde00) = -1 ENOENT (No such file or directory)
[pid 17444] stat("/usr/share/julia/environments/v1.0", {st_mode=S_IFDIR|0755, st_size=242, ...}) = 0
[pid 17444] stat("/usr/share/julia/environments/v1.0/JuliaProject.toml", 0x7ffe0d5fde00) = -1 ENOENT (No such file or directory)
[pid 17444] stat("/usr/share/julia/environments/v1.0/Project.toml", 0x7ffe0d5fde00) = -1 ENOENT (No such file or directory)
[pid 17444] stat("/home/jonathon/.julia/environments/v1.0/Project.toml", 0x7ffe0d5fdf80) = -1 ENOENT (No such file or directory)
[pid 17444] stat("/home/jonathon/.julia/environments/v1.0/Project.toml", 0x7ffe0d5fdf80) = -1 ENOENT (No such file or directory)
[pid 17444] stat("/usr/share/julia/stdlib/v1.0", {st_mode=S_IFDIR|0755, st_size=460, ...}) = 0
[pid 17444] stat("/usr/share/julia/stdlib/v1.0/JuliaProject.toml", 0x7ffe0d5fdf80) = -1 ENOENT (No such file or directory)
[pid 17444] stat("/usr/share/julia/stdlib/v1.0/Project.toml", 0x7ffe0d5fdf80) = -1 ENOENT (No such file or directory)
[pid 17444] stat("/usr/share/julia/stdlib/v1.0/IJulia.jl", 0x7ffe0d5fdf80) = -1 ENOENT (No such file or directory)
[pid 17444] stat("/usr/share/julia/stdlib/v1.0/IJulia/src/IJulia.jl", 0x7ffe0d5fdf80) = -1 ENOENT (No such file or directory)
[pid 17444] stat("/usr/share/julia/stdlib/v1.0/IJulia.jl/src/IJulia.jl", 0x7ffe0d5fdf80) = -1 ENOENT (No such file or directory)
ERROR: ArgumentError: Package IJulia not found in current path:
- Run `import Pkg; Pkg.add("IJulia")` to install the IJulia package.

Note that it no longer looks in subdirectories under the path /usr/share/julia/environments/v1.0/.

I am currently investigating eb8a933 and 71748da as potentially related but I don't really know if they are.

Julia distro package: https://www.archlinux.org/packages/community/x86_64/julia/

julia> versioninfo()
Julia Version 1.0.2
Commit d789231e99 (2018-11-08 20:11 UTC)
Platform Info:
OS: Linux (x86_64-pc-linux-gnu)
CPU: Intel(R) Core(TM) i7-3630QM CPU @ 2.40GHz
WORD_SIZE: 64
LIBM: libopenlibm
LLVM: libLLVM-6.0.0 (ORCJIT, ivybridge)

julia> versioninfo()
Julia Version 1.0.3
Commit 099e826241* (2018-12-18 01:34 UTC)
Platform Info:
OS: Linux (x86_64-pc-linux-gnu)
CPU: Intel(R) Core(TM) i7-3630QM CPU @ 2.40GHz
WORD_SIZE: 64
LIBM: libopenlibm
LLVM: libLLVM-6.0.0 (ORCJIT, ivybridge)

Mainly for my own reference, full list of changes between 1.0.2 and 1.0.3: v1.0.2...v1.0.3

Issue 2:
I'm using Julia Version 0.5.0 (2016-09-19 18:14 UTC) and noticed that in a comprehension you can't iterate over empty sequences unless that variable is the last one. (EDIT: I just tested in the binaries of the nightly builds and the same thing happens.)

I'd expect both of these comprehensions to result in empty arrays:

julia> [a for a in [1] for b in []]
0-element Array{Int64,1}

julia> [a for a in [] for b in [1]]
ERROR: ArgumentError: argument to Flatten must contain at least one iterator
in start(::Base.Flatten{Base.Generator{Array{Any,1},##193#195}}) at ./iterator.jl:599
in grow_to!(::Array{Any,1}, ::Base.Flatten{Base.Generator{Array{Any,1},##193#195}}) at ./array.jl:357
in collect(::Base.Flatten{Base.Generator{Array{Any,1},##193#195}}) at ./array.jl:273

Or a list of triples (a,b,a+b) where 1<=a<b<5 and a+b is prime:

julia> [(a,b,c) for a=1:5 for b=a+1:5 for c in [a+b] if isprime(c)]
ERROR: ArgumentError: argument to Flatten must contain at least one iterator
in start(::Base.Flatten{Base.Generator{UnitRange{Int64},##18#21{Int64}}}) at ./iterator.jl:599
in next at ./iterator.jl:614 [inlined]
in grow_to!(::Array{Tuple{Int64,Int64,Int64},1}, ::Base.Flatten{Base.Generator{UnitRange{Int64},##17#20}}, ::Tuple{Int64,Base.Flatten{Base.Generator{UnitRange{Int64},##18#21{Int64}}},Tuple{Int64,Base.Generator{Filter{#isprime,Array{Int64,1}},##19#22{Int64,Int64}},Tuple{Bool,Int64,Int64}}}) at ./array.jl:364
in grow_to!(::Array{Union{},1}, ::Base.Flatten{Base.Generator{UnitRange{Int64},##17#20}}, ::Tuple{Int64,Base.Flatten{Base.Generator{UnitRange{Int64},##18#21{Int64}}},Tuple{Int64,Base.Generator{Filter{#isprime,Array{Int64,1}},##19#22{Int64,Int64}},Tuple{Bool,Int64,Int64}}}) at ./array.jl:372
in grow_to!(::Array{Tuple{Int64,Int64,Int64},1}, ::Base.Flatten{Base.Generator{UnitRange{Int64},##17#20}}) at ./array.jl:357
in collect(::Base.Flatten{Base.Generator{UnitRange{Int64},##17#20}}) at ./array.jl:273

Oops, that last value of a let to an empty range for b, better skip it:

julia> [(a,b,c) for a=1:4 for b=a+1:5 for c in [a+b] if isprime(c)]
5-element Array{Tuple{Int64,Int64,Int64},1}:
(1,2,3)
(1,4,5)
(2,3,5)
(2,5,7)
(3,4,7)