sys: fsmup device

- This commit introduces the fsmup device, which is a major change in how
network file systems are handled. Previously every network file system's
fsvol device was directly registered with the MUP. Now there is a single
fsmup device that is registered with the MUP; network file systems' fsvol
devices register with fsmup instead. The fsmup device maintains a prefix
table which it uses to demultiplex and forward requests to the appropriate
fsvol device.
- This device change was necessatitated to fix issue #87.

build/VStudio/winfsp_sys.vcxproj

@@ -173,6 +173,7 @@
     <ClCompile Include="..\..\src\sys\ioq.c" />
     <ClCompile Include="..\..\src\sys\lockctl.c" />
     <ClCompile Include="..\..\src\sys\meta.c" />
+    <ClCompile Include="..\..\src\sys\mup.c" />
     <ClCompile Include="..\..\src\sys\name.c" />
     <ClCompile Include="..\..\src\sys\psbuffer.c" />
     <ClCompile Include="..\..\src\sys\read.c" />

build/VStudio/winfsp_sys.vcxproj.filters

@@ -101,6 +101,9 @@
     <ClCompile Include="..\..\src\sys\psbuffer.c">
       <Filter>Source</Filter>
     </ClCompile>
+    <ClCompile Include="..\..\src\sys\mup.c">
+      <Filter>Source</Filter>
+    </ClCompile>
   </ItemGroup>
   <ItemGroup>
     <ClInclude Include="..\..\src\sys\driver.h">