no completion for stl's method when PWD is folders except /tmp

## Problems summary
I noticed that method completion fail to show for STL's variable, however it works when in /tmp. Methods for struct and class and all other type of completions I can think of work everywhere though.
For example the following:
```
#include

using namespace std;

int main(void)
{
vector vec;
vec.
}
```

## Expected
Completion of methods for vector pops out. However there's none when current working directory is folders like `~` or `~/anynamesitried`; but when pwd is /tmp it works as expected. (I noticed this occasionally)

## Environment Information

- OS: arch linux
- Neovim version:
NVIM v0.2.1-824-g5566f3000
Build type: Release

## Provide a minimal init.vim with less than 50 lines and not plugin manager (Required!)

```vim
set runtimepath+=~/path/to/deoplete.nvim/
set runtimepath+=~/path/to/deoplete-clang/
let g:deoplete#enable_at_startup = 1

let g:deoplete#sources#clang#libclang_path="/usr/lib/libclang.so.4.0"
let g:deoplete#sources#clang#clang_header="/usr/include/clang"
```

## The reproduce ways from neovim starting (Required!)

# init.vim in ~/test
1. `cd ~/test`
2. `nvim -u init.vim asdf.cpp # above contents`
3. completion not work.
4. :wq
5. `cd /tmp`
6. `nvim -u ~/test/init.vim ~/test/asdf.cpp`
7. completion work.

## Generate a logfile if appropriate

when in /tmp: http://lpaste.net/358100
when not in /tmp: http://lpaste.net/358101

## extra information
The file structure for clang's include path seems to be changed if I remember correctly. Now it looks like:
```
λ /u/i/clang ls
Analysis AST Basic Config Edit Frontend Index Parse Sema StaticAnalyzer
ARCMigrate ASTMatchers CodeGen Driver Format FrontendTool Lex Rewrite Serialization Tooling
```
which is different from what is show in README.md, the path contains those files is `/usr/lib/clang/4.0.1/include`, I tried this path for *clang_header* but its the same.
```
λ /u/i/clang ls /usr/lib/clang/4.0.1/include
adxintrin.h avx512ifmaintrin.h __clang_cuda_builtin_vars.h fma4intrin.h mm3dnow.h rdseedintrin.h stdint.h x86intrin.h
altivec.h avx512ifmavlintrin.h __clang_cuda_cmath.h fmaintrin.h mmintrin.h rtmintrin.h stdnoreturn.h xmmintrin.h
ammintrin.h avx512pfintrin.h __clang_cuda_complex_builtins.h fxsrintrin.h mm_malloc.h s390intrin.h tbmintrin.h xopintrin.h
arm_acle.h avx512vbmiintrin.h __clang_cuda_intrinsics.h htmintrin.h module.modulemap sanitizer tgmath.h xray
armintr.h avx512vbmivlintrin.h __clang_cuda_math_forward_declares.h htmxlintrin.h msa.h shaintrin.h tmmintrin.h xsavecintrin.h
arm_neon.h avx512vlbwintrin.h __clang_cuda_runtime_wrapper.h ia32intrin.h mwaitxintrin.h smmintrin.h unwind.h xsaveintrin.h
avx2intrin.h avx512vlcdintrin.h clflushoptintrin.h immintrin.h nmmintrin.h stdalign.h vadefs.h xsaveoptintrin.h
avx512bwintrin.h avx512vldqintrin.h cpuid.h intrin.h opencl-c.h stdarg.h varargs.h xsavesintrin.h
avx512cdintrin.h avx512vlintrin.h cuda_wrappers inttypes.h pkuintrin.h stdatomic.h vecintrin.h xtestintrin.h
avx512dqintrin.h avxintrin.h emmintrin.h iso646.h pmmintrin.h stdbool.h __wmmintrin_aes.h
avx512erintrin.h bmi2intrin.h f16cintrin.h limits.h popcntintrin.h stddef.h wmmintrin.h
avx512fintrin.h bmiintrin.h float.h lzcntintrin.h prfchwintrin.h __stddef_max_align_t.h __wmmintrin_pclmul.h
```
There's no path looks like `something/clang/` which also contains those header files in my system. Can this possibly the reason for this strange behavior? I have no clue why the above happens.
Feel free to ask if you need any further information :)