Auto merge of #466 - Valloric:ubuntu-fix, r=micbou

[READY] Storing path to Python used in build.py

We'll use this in YCM to ensure we start ycmd with the same version of
Python that was used for building the C++ libraries loaded into ycmd.

Related to ycm-core/YouCompleteMe#2136

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.gitignore

@@ -38,6 +38,7 @@ nosetests.xml
 
 # custom
 ycm_core_tests
+PYTHON_USED_DURING_BUILDING
 
 # When we use the bcp tool to copy over the parts of boost we care about, it
 # also copies some cruft files we don't need; this ignores them

build.py

@@ -427,6 +427,12 @@ def SetUpTern():
   subprocess.check_call( [ paths[ 'npm' ], 'install', '--production' ] )
 
 
+def WritePythonUsedDuringBuild():
+  path = p.join( DIR_OF_THIS_SCRIPT, 'PYTHON_USED_DURING_BUILDING' )
+  with open( path, 'w' ) as f:
+    f.write( sys.executable )
+
+
 def Main():
   CheckDeps()
   args = ParseArguments()
@@ -440,6 +446,8 @@ def Main():
     SetUpTern()
   if args.racer_completer or args.all_completers:
     BuildRacerd()
+  WritePythonUsedDuringBuild()
+
 
 if __name__ == '__main__':
   Main()